A few other thoughts --
We should separate Iraqi culture from Arabian. This would be consistent with the other divisions among the Arabs and probably would increase realism just in preventing specific regimes from easily overexpanding in Arabia and Iraq. Iraqi is a better name than Mesopotamian -- in the time frame of our game, "Iraq" referred to a more broad geographic region which would include Khuzestan. http://en.wikipedia.org/wiki/Persian_Iraq
On cultures of the Ottoman Empire, my strong leaning at present (after rather exhaustive reading on these subjects) is for the Ottomans to begin with only Turkish in 1419, and gain Greek, Sephardi (a new culture; my idea at present is for the Salonika province to become Sephardi by event coinciding with Jewish migration and opening of a trade center), Bosnian, and Albanian. This is definitely a tough position for Ottomans, but I think it's the most realistic portrayal. I'm recommending they never receive Bulgarian, and effectively never receive any eastern Muslim cultures in conquered areas -- above discussions indicate this will not hurt the Ottomans in any crippling way as the vast majority of these provinces would be Sunni; I'm proposing we use the opportunity presented to more properly represent the relative degree of integration of peripheral areas of Ottoman territories.
(If we absolutely need to give Ottomans Levantine and Kurdish in the short-term during testing toward rebalancing I'm sure that would be fine, but I think it's simply not accurate or representative to be handing the Ottomans any additional cultures beyond these and we should consider it ultimately not especially plausible for them to receive either Levantine or Kurdish, just more plausible than, for instance, Egyptian, and ok for a "training wheels" phase of testing and rebalancing in which we're weaning Ottomans from having so many culture.)
We should have Ottomans gain Greek as an accepted culture by event after conquest of Constantinople if Ottomans allow Patriarchate to continue (which happens in two of the three choices in that event at present) -- historically, this is in line with a major social reason why Greeks had relative privileges among Orthodox Christians (Greek administration of the Church put them very near Ottoman power). I still don't think Greek is even a definite or clear-cut case for an accepted culture for the Ottomans, for a lot of reasons, but there should be some representation of the relative economic status of Greeks in the Balkans vis-a-vis the Serbs and Bulgarians, and I think the only way to represent that in a plausible gameplay sense is for Ottomans to receive Greek culture around 1453. But we should make most Greek provinces extremely hard to convert (and make most provinces in the Balkans that did not historically convert more difficult to convert than at present). Ottomans should probably lose Greek culture in 1774 (which is near when they lose it at present in game terms) with a historical parallel to make use of in terms of Russia claiming protectorship over Orthodox Christians and so the special relationship between Ottomans and Greek clerical hierarchy losing its meaning (this being only one event among many signifying emergence of a Greek nationalism, but appropriate as the trigger for an event for our purposes).
Ottomans would receive Sephardi around 1492 or whenever the specific events involving Salonika would fire. We should add a Jewish religion for this one specific province; this would give Ottomans another internal religion to balance for regarding tolerance sliders and in creating this additional difficulty properly represent how religious community tensions (particularly Jewish vs. Orthodox) had a destabilizing effect on long-term Ottoman success.
I actually think Bosnian provinces should begin game as Serbian, but become Bosnian by event sometime in the mid 1500s along with those provinces converting to Sunni. Ottomans should gain Bosnian as an accepted culture at same time provinces become Bosnian.
Albanian is actually a complicated case because for roughly the first half of our game they should be one of the least integrating cultures in the Balkans for the Ottomans; I'm not sure Ottomans should gain Albanian as an accepted culture before around 1600 or slightly later.
Would these changes "imbalance" things? Maybe, but I'd say if we're putting forward our efforts we should have some faith in the ability of our engine to properly represent history; there are also vast correspondent steps we can take to balance things in favor of the Ottomans to ensure their viability or strength as a regime. Basically, the goal should be: represent Ottoman power and complexities of the Ottoman system more accurately without imbalancing the game. This would seem to entail striving for maximum accuracy first, and then rebalancing from that when and if necessary.
Immediately these changes come to mind -- I think a balancing and better representation of history occurs if we have the provinces of Thrace and Rumelia both begin as Turkish culture. Mass Turkish migrations were already occurring to these provinces by the late 1300s; Plovdiv was majority Turkish by 1400. I think it's probably ok for Thrace to begin as Turkish and Orthodox (ie, representing a Turkish plurality, but combined Orthodox majority between Greeks and Bulgarians) but for Rumelia to begin as Turkish and Sunni. This helps Ottomans remain viable early on without Bulgarian culture. Thrace and Bursa should start with tax collectors and at least Thrace should begin with a small fortress. Macedonia should begin game as Bulgarian and Salonika should begin as Greek (and turn Sephardi through event if owned by Ottomans); Macedonia should begin with a small fortress and Salonika with a large fortress (to properly simulate the difficulty of conquering it in the 1420s and then giving the Ottomans a powerful base if/when they conquer it -- I'm thinking possibly an event can force Ottomans into a war with Venice, and then a script could check to see if Ottomans control Salonika at any point during that war, they automatically annex it, and Venice should receive no core over the province anyway). I'm all in favor of using events to "steer" Ottoman power in the historically correct direction and this could sometimes include new events that grant stronger fortresses, etc, as a way to balance for Ottomans or properly represent the nature of their power relative to others. And so my thought on Macedonia and Salonika is that both of them should gain +1 fortress alongside Jewish migration events which also turn Salonika into a trade center. This would basically involve giving the Ottomans what in game terms would function almost as a completely "new" province (Salonika) which would be one of the wealthiest and strategically-difficult to conquer cities along the entire Mediterranean coast, so changes I'm proposing that would seem to "weaken" the Ottomans should be considered in context with the changes which would strengthen them.
Dobruja can become Turkish by event sometime also.
At present I think the trade center which would move to Salonika should actually begin in Achaia at Patras -- from trying to read a lot on the subject, it seems to me that Latin controlled trade in Greece emerging out of the post-Fourth Crusade early finance imperialism was definitely multi-centered but that Patras is as good of a choice as any in terms of granting one province that status in the early part of our game. And so this also makes Achaia a more strategically important province early in the game. I would also remove the ports from Morea and Attica (and Attica should actually probably be Albanian rather than Greek if we want to be as accurate as possible -- Albanian presence in various parts of Greece, especially Epirus and Euboea, had areas which were majority Albanian; to represent and balance, one of the provinces which is now Greek should be Albanian and Attica seems to have the strongest demographic case for that (in that Athens itself was such a small city in the time period of our game and the rural areas around it were definitely majority Albanian).
CoT in Patras would close and move to Salonika if proper events fire when Ottomans control Salonika. So basically what I'm proposing with CoT's in the Ottoman sphere would be for them to begin at Patras and Kaffa; Kaffa CoT moves to Istanbul when Ottomans conquer it. Patras CoT moves to Salonika when Ottomans have Jewish migration event. CoT's stay stable at Salonika and Istanbul for some time, then CoT in Istanbul closes and a CoT opens in Smyrna at the proper historical interval.
Also, in determining just sort of what type of basic "thing" the Ottoman Empire was, I almost wonder if it would be appropriate to consider (and be relatively non-difficult to implement) some type of basic event that happens anytime Ottomans conquer a non-Muslim province which they have claim or national core over -- that is, anytime Ottomans conquer a new Christian province in Europe for the first time, an event can fire saying something like "(Name of province) has submitted to dhimmitude!" which will see Ottomans gain 100 or 150 gold and maybe gain 1000 infantry somewhere, but the province itself have -1 or -2 tax value happen. This essentially properly represents the power of the Ottoman Empire "front-loaded" into the earlier centuries of our game, essentially as a sort of "forward-looting empire" which gained massive power and wealth through early conquests but ultimately lacked an appropriate system of economic organization to effectively administrate all conquered areas permanently. General rebalancing along with implementation of this style of continuing "conquest" event would seem to portray Ottoman power over time in about as effective of terms as possible with the variables available for our use.
One or two other thoughts while I'm posting this now -- Aleppo was one of the most populous cities in the Ottoman Empire, which we don't represent at present. Strengthening some individual provinces such as Aleppo would also serve to properly balance Ottomans, and if we manage to rework provinces in Syria and elsewhere in the way I've proposed, it would also be a good excuse to look more closely at population, manpower, and tax values throughout the OE and re-calibrate appropriately.
On this subject, Palestine should also not have a port in the time frame of our game, and I think we should be extremely deliberate in decisions to place ports; we may find in being more sparing in placement of ports creates a more accurate, fun, compelling naval game for a country like the Ottoman Empire. Mecca should have a port at Jeddah, but Medina should not have an effective port in our game's time frame. (I have other ideas on how to handle Red Sea ports.)
I'll post the maps I have in mind regarding Egypt and North Africa now:
Egypt: Attachment 70966
I could put forward a more extended defense of this map if necessary, but I'm entirely certain it vastly improves on our present map of Egypt while using the same number of provinces. Only Alexandria and Suez should have ports. Relative population of different parts of Egypt, and the general types of administrative boundaries that were actually used in this time period, and general geostrategics of the area, are all much more accurately represented in the map I've drawn. North of Cairo is Damietta (province is on coast but should not have a port); east of Cairo is Suez (with port, possesion of which should be the focal point of specific triggered events regarding Ottoman Indian Ocean expeditions); south of Cairo is Luxor or whatever we'd want to name that province. Faiyum and Asyut are in the same place. Major CoT in Alexandria throughout the game, and Cairo should be a very important economic center for Ottomans also if they hold it.
North Africa: Attachment 70967
Certain province placement is flat-out incorrect on our present map, and so this is an attempt at improvement on accuracy with tweaks toward better gameplay as well. It wouldn't be clear on this map, but I'm intending Djerba to be a separate province -- this map keeps the same number of provinces as our present map and both represents history more accurately and creates a foundation for greatly improving the Mediterranean game as it stands now in terms of Ottomans vs. Spain and creating a better game board for anything that would happen in game terms.