I had installed patches and also the xp remover for SoA, If I install ToB will there be any problems when transfering my characters to ToB?

One more advice,
I'm at Chapter 4, if I install ToB, what it effects my game except TAB function and Watchers Keep? I can get to Watchers Keep also from ToB, so the expansion will not ruin my Soa game right? Or should I install it before I complete the game?

If you install TOB during a current BG2 SOA game, it will give you the initial option of playing either. So (as far as i know) you can carry on with SOA including the Watchers Keep all the way throught to the end of TOB. The game option to start TOB instead of SOA merely starts the game from the beginning of TOB giving your character a set exp level if a new character, or you can simply import your saved character from your saved game SOA

So I can install it after I completed the game right? If it does not effect add items quests etc