I think I can answer some of them.
1) Lords are kings of their regions. They get to decide what stays and what doesn't.
2) I wouldn't mind seeing some changes to enlarging temples to allow lords to be able to enlarge them as well as long as they are a part of that religion. We no longer have too many people playing priests and most religions have one or two at most. Priests can't be everywhere.
For now though, lords are not in charge of maintaining temples. Priests are. They are the ones paying the maintenance fee not lords.
3) It is there to prevent intentional abuses. If you allow an easy way to transfer gold, people will use temples to replenish their gold.
4) It looks pretty when you have a large temple. Also, large temples can help you maintain large followers. Does it have any benefit for a region to actually have one? No. Religions don't really have that big of an impact mechanically if you just think about temples alone.
5) Priests are annoying pests at most for lazy lords. Don't bother with them. They won't allow you to build a temple ever.
6) No.
