The Tavern

How difficult would it be, coding wise, to reduce the size of generated levels? I think Circus Animals (?) had bigger than normal levels? I want to go the opposite route.

Also, I think that there are some full-level vaults (like the one in Crypt which is in the shape of skull and bones) which might need change or removal. How do I find out which are full-level vaults?

Levels are created by picking one of several "layout" functions and running it. This places generates all the base-layer terrain and then (optionally) places vaults on top of it. Nobody has modified any of those layout functions for a loooong time, so you would probably need to learn the code from scratch yourself.