Are we allowed to sell other things, like character points (give me some mush and I'll give character points to your wolf)?

Are we also allowed to "borrow" wolves (give me some mush and I'll take care of your wolf for some amount of time)?

"Borrowing" wolves, according to your definition, is usually called boarding. You can do it, but it is not supported by staff and any problems you encounter you'll have to deal with yourself.