Does anyone know whether"BG1 Adventure Pack" and "BG1 CoM Forge/Item Upgrade Mod" are compatible with this the mega-install?
No. or not yet they are still a BG1 mods not BGT or Tutu.
No.What's about Improved Anvil?
It can. It has worked for me, I think it overwrites some areas not extends, so you might want to install early.Same question for CoM Encounters.
Some of it, it mostly already is in BP. Read This.What's about Tactics?