Step 0: Always watch for the Ottoman armies to cross the Straits of Constantinople into Asia. You'll be looking to strike when the Ottomans are all in Asia, utilizing a superior navy to keep their armies trapped in Asia while you besiege their Greek territories. As you do the rest of these steps, keep an eye out for the Ottomans, especially their progress against the Timurids; that is usually the deciding factor in when to strike. Also, this requires some luck. It's okay to restart if you get an early (i.e. before the first two attacks, on Epirus and the Ottomans) Regency Council or other seriously unlucky happenings.
Step 1: Load your infantry onto your transports, move adjacent to Epirus and DOW with Reconquest CB the day after Naples does. You'll be able to land first if you don't waste a single day. Use the Neapolitan troops to help you win the siege and raise War Taxes, but do NOT annex until you're about to get forced into a white peace; you want the War Taxes for as long as possible.
Step 2: After getting to +3 Stability, set your treasury slider to full mint and do not pull it off until you attack the Ottomans the first time. You should be able to afford ~2-3 galleys per year. Build them and cogs until you have about 3 of each to the Ottomans' 2; the Ottomans usually build about 14/6 so you're looking at 20/10. Once you're done with that, build as many infantry (favoring Muslim infantry if they're available in Epirus, as they sometimes are; then Western infantry; then Eastern) as you can afford on full mint without accruing an annual deficit.
Step 3: After doing all of this, pull back the treasury slider as much as possible without accruing an annual deficit, put your fleet in the Sea of Marmara and attack the Ottomans the instant their armies are in Asia. You may find Serbian or Bosnian troops still in Europe, but they don't field more than about 3000 apiece, so your army should be able to handle them. Typical result is to see Byzantium reclaim all Ottoman Europe provinces except Edirne; if the Ottomans end up losing to the Timurids while you're beating them, you might be able to cross the straits and take Turkish provinces. If any patriots aligned with you pop up in Ottoman territory, let them seize provinces and let the provinces defect; no need to waste war score.
Step 4: At this point, you're sufficiently on par with the Ottomans that you can afford to play more like a normal country (that is, not mint heavily to survive). Try to get a Master of Mint and the National Bank NI immediately to work off inflation, and focus on getting a solid foothold in Turkey from the second war with the Ottomans. The third war should see their annexation; this third war can be deferred since the second one will end the Ottomans as a threat to you, and should be deferred if you're past about 1535 or so, to give yourself time to recapture your Turkish cores from Ramazan et al (since those expire). Ignore any more Greek cores for right now. Important note for later: On the second war with the Ottomans, try to get Bosnia and Serbia de-vassalized. They stay allied with the Ottomans, so on the third war they should still come fight you, at which point you can vassalize them yourself.
Step 5: Once you own your ex-Ottoman cores and your Turkish cores, look around. You'll probably have to wait on Venice and vassals/puppets because you still won't be particularly wealthy and you'll need to be if you intend to field the requisite fleet to beat Venice. If you see something like Trebizond, an unprotected (i.e. expired guarantee) Greek/Crusader minor, pick them off. If you see someone like The Knights, which usually keeps no more than about 2000 troops, send a few Patriot spies if you have the money and let it defect. Basically, start slowly building up money to afford a respectable fleet (because galleys and cogs sure aren't) and looking for any opportunistic core snatches.
Step 6: Once you have the requisite navy, smash Venice. 100% war score should be more than sufficient to get Corfu, Naxos, Crete, Albania and Athens. If any of the above provinces are still owned by Venetian vassals instead of Venice, attack them and Venice with the Reconquest CB on the same day; doing so will keep the vassal as the war leader and allow for annexation.
Step 7: If you're reading this having made it through 1-6 in-game, congrats, you're on your feet. Outro note: Hordes suck. Watch your borders carefully, and ally with a vassal which does not border a horde; successful use of that trick can keep the Horde from ever attacking you.
