Thank you, I didnt know the last part. How hard is it to get that to happen and how soon will it happen?
It's quite easy. There's a couple things you can do to gain IA. Make HRE nations release other HRE nations they annexed. Force convert other HRE nations to your religion. Add provinces to HRE. Release nations (can be as vassals) that now are on HRE (i.e.: annex Naples, add all Naples provinces to HRE, release Naples as vassal).
That can be done as early as 1520, but if you get it by 1600 is good enough.
What are the best ideas for the Ottomans ? I would go Dilpomatic>Religious>ADM (dont like double ADM ideas though)
1st idea: Diplomatic
Must have, best way to spend your early points because diplo tech doesn't mean much to Otto.
2nd idea: Defensive/Offensive
Pick your choice. At this point you should have an excess of mil points, if you don't wanna waste it, better use it on ideas to make your conquest easier.
3rd idea: Admin/Religious
Admin is really good for you to go on a core spree. Probably the best idea for Otto, you can even push it as 2nd idea. Religious if you're playing a more vassal-feeding kind of game. It'll give you religious casus belli that will trigger op Ghazi.
4th, 5th, 6th: Admin/Religious, Expansion, Innovative/Aristocratic/Exploration (not necessarily in that order)
Pick the one you didn't choose as 3rd. Expansion is a must have for the casus belli against east asia and a couple nice bonuses. Now it's the last choice, Innovative for some nice events and bonuses, Aristocratic for the extra diplomat, WE cost and mil tech cost, or Exploration for the colonists and casus belli against american nations.
7th, 8th: doesn't matter. It's too late, pick whatever you want.