1) Yes, the door can only be opened in HOW
2) For some reason most of them just stand around, but if you talk to some of the kids on the first level after killing the Lizard King, they'll thank you, giving you some exp.
3) Yep, those are all the items there are. In HOW, once the priest gets all 4 items he'll thank you and vanish, but in IWD he just stands around like a dummy
-Wrath