This mod is fantastic! You just gotta love the fief system. It gives you a real feel how a feudal lord felt, defending his lands from constant attacks of his neighbors. I also really like the arms and armour you've picked for the units, gives a really realistic kick to the game.
Just a few suggestions, could you get some armoured horses in, for both arabs and byzantines?
Second, i would love to see an even more complex system of politics. So, i suggest tweaking down the rate of spawning of new vassals and their retinues. You should also allow some rudimentary form of diplomacy between enemies. So you could promise one of the enemy lords help fighting his neighbor or whatever.
Apart from the mentioned bugs(darn castle bug :/), i think you should remove the random city market spawning. It's very annoying, at least to me.