Ok here we go!
1.If you mean the items like moondial,boots,water ect then placing them in the "correct" statue will give you a dusty rose ioun stone and one of thegems needed for the room with the portal.
2.Yep.You need three gems.One gives you a greater wolfwere to figt,one a demon and one a djin which is not hostile and rewards you with Doomplate +3
3.In the room where you fight the kobolt avatar.
4.Of course!
5.You fight monster with increasing difficulty.The last one is a Beholder.Then you get simulacrum,summon fiend and ring of free action
6.with 5 tokens you get boots of the north
with 10 boots of grounding
with 15 boots of speed
with 20 Jester's chain+5
7.Sigh I don't seem to recall this now.Sorry!