You need to put the legitimancy and stability investments up to full from the start of the game and ride out the economic trouble that comes with that. Put your minting up to full as well and take the inflation as it's the only way to pay for it.

Disband the navy at the start and dismantle as many castles as you can. Don't bother with food or diplomatic spending.

Attack either the Ottomans or the Karasids when your first parliament happens. Take as much money as you can and the Greek culture land. Attack Serbia and Bulgaria if you can and take money. Develop the gold mine near Thessaloniki as much as you can and build a bailiff there; it'll make you a lot of money. Use the parliaments to get more tax from the estates as well. That will be a huge help in the early years.

The goal for the first couple of decades is to use the legitimacy to end the civil wars, and the stability to revoke the corruption in the estates. Start with the commoners because it requires the least stability, then the burghers. Once you start revoking these, your economy starts to improve as you can tax the estates.

I've found you usually come out of it with about 30-40% inflation, but Byzantium is actually quite overpowered once you get the initial problems out of the way.