8) They're already collapsing like there's no tomorrow. I'll think about it
For the Byzantines or for the Arabs; I strongly recommend that u somehow let the Arabs retain Baghdad. Although on the maps it shows Baghdad to be part of Seljuk Territory I would like to point out that they were definitely not. Their relationship to the Seljuks was like Papal states to HRE or France.
Here is my idea; As soon as the Seljuks conquer Baghdad; the Abbasids collapse but Baghdad respawns the same turn as a vassal state to the Seljuks exercising control of Baghdad and its surroundings while Seljuks control everything else.