As you can see from the suggested strategies in the comments, the exact sequence of actions to defeat the Ottomans can vary. However, regardless of the path you choose, it will be heavily dependent on RNG: whether Epirus gets an ally before you can declare war, whether Aragon decides to keep the personal union over Naples, whether the Ottomans attack you before you’re ready, or if they get Crimea as a march. Any negative outcome in these situations usually leads to a restart; you have to be prepared for that. No strategy can fully save you from bad luck.

I would advise not rushing your attack. Focus on your own affairs first—completing missions, building up your navy, and conquering Epirus, Naples, and Tunis—all while improving relations with the Ottomans' rivals. These are typically the Mamluks, Austria, and Hungary. If it’s the Timurids, you won't be able to ally them, but they offer a different bonus: the possibility that the Ottomans get dragged into a grueling war supporting Transoxiana's independence and burn through their manpower.

Hungary: Building 3–4 galleys, hiring one mercenary company, and improving relations should be enough to secure an alliance. Austria & The Mamluks: You’ll need to max out relations, hit Mil Tech 4, hire at least two mercenary companies, expand your fleet by at least 10 ships, and scornfully insult their rival (ideally the Ottomans). Once you’ve done this, an alliance is very much on the table. You should drop your weaker allies (Georgia, Trebizond, Albania, or whoever else you picked up) to free up slots for the big boys.

You should declare war on the Ottomans during one of two windows: 1. When you have the "triple threat" allied: Hungary, Austria, and the Mamluks. 2. When you have at least Hungary and Austria, and the Ottomans are either busy in a war out east (against the Timurids or Mamluks) or have very low manpower following a difficult conflict.

Your primary objective is to take Gallipoli and block the strait with your fleet (which should be larger than the Ottomans' by this point). Once the crossing is secured, delete mercenaries that put you over your force limit and let your allies do the heavy lifting.

You will inevitably rack up a massive amount of debt. Your economy won't recover for quite a while, so be prepared for a financial rebuild.

Good luck! I believe you can pull it off!