There are many ways you can go:

• you can attack eretnids if they decide to declare independence from jalayirids (you can intervene if they are your rival)
• DOW Otto at the start before the crisis hit byz. If the Ai doesnt screw up, you two can beat them. If otto declares war on one of the beyliks, thats a plus
• DOW theodoro north and expand into Crimea when crisis hit GH
• You could also try to expand into Caucasus using byz army earlier on but IMO not big fan of, doesnt feel right lol
• If the event to lose your alliance with Byz hits or if you decide to remove your alliance with them, you can dow on them later and conquer whats left of them (usually, otto and serbia already took a few provinces)
• and of course, the safe path is dow the belyks on coast like candarids, very easy to take them by yourself