1) Useful Cilent States.
My main issue with them is that they are almost never a good idea when taking land is simply more pratical. Most people only ever use them as border defence, but even then it just makes it messy when you have to murder them take the land, even if they are your best friend at that point. Annexation without bloodshed would be lovely, though ideally only if they really like you. Also the tribute they send you should depend on how much they like you. More love more money!

2) More Unquie Units for Factions
Pretty sure we all know this one. Personally think English Factions shouldn't even have axe infantry and their cavalry should be A LOT better. I'll leave the rest to the people with skills.

3) Monastery In England!
I get they were probably trying to split up resources so they were more valuable. But I don't see any logic in there not being a Monastery in England and only being in Scotland and Ireland. I think Wessex should at least have one. 3 throughout the map would be pretty reasonable.

4) No Catapults Mod and or Ladders instead of Siege towers.
I'm fairly certain they wouldn't have been using siege towers during that time, or at least not when Ladders could do the job just fine. As for Catapults, I haven't heard much about them being used during the period, though I'm no historian.