Religious and quantity ideas are a must for Byzantium. Naval forcelimits will be important too especially late game when you'll likely be fighting a lot of wars with Spain as they tend to nab parts of North Africa besides their Italian holdings. Manpower is not going to be an issue, I figure even without Quantity you'll have plenty to spare.
Funny that when you start the game, winning your first war against Ottomans is actually the easiest part. The actually hard part comes when you are going to attack Anatolia, that can go badly wrong if you have bad timing/RNG.
I was myself stopped in Italy. I fought three wars against Austria/HRE and never got through, eventually I gave up and dug in.
With my Italian ambitions more or less dead thanks to a huge Brandenburg blob who likes to cooperate with Austria, little I have left than finishing off northwestern Africa and expanding my turf in India where I recently gained a foothold on the Indus river.
I'm very happy at how those Tunisian/Libyan minors turned out. I freed them from Tunisia, I could have conquered them but wouldn't have made as pretty borders as just taking the coast.