I finally dled the scen
It looks very nice, and i ahve played almost ten turns as the byzantines.
The idea to link bulgaria and serbia with the seljuk sultanates was not perfect, but i see your point. However it should be noted that near the end of the Byzantine Empire there had been attempts for all the christian kingdoms of the region to unite against the ottomans, and possible delay in the ottomans declaring war on the other seljuks would make that impossible. Atm i have conquered two cities in epiros from the serbs, and lost two cities to the ottomans.
-Sea trade seems to be disabled; why so? (unless the building that allows it is not available yet)
-The Byzantine empire starts at war with the principality of Corinth and the Dutchy of Athens, principality of Cephalonia (in your scen those are united as latin duches). This too can become destabilising, particularly since those duchies are united unlike what they were.
-The varangian guard was not around after 1204 (at least not in any significant number of units and formations, and definately not as the strong guard of Constantinople)
-Philadelphia should have been more fortified/guarded; it was a lot more difficult to be conquered
-While i see why you have the ottomans in locked war against the Byzantine Empire, this was not at all the case. Infact the spread of Serbia in the lower balcans under Steven Dusan caused the Byzantines to bring the Ottomans into the conflict, so that they could utilise more troops against the serbs.
All in all the scenario looks fun to play