[Greg.]

How much in the way of choice are you going to have? Being able to choose who stays in your town and what services are offered would be cool...

Perhaps an alchemy garden - where you can grow different plants for ingredients - would be a good idea. A bit like the one in the wizards tower mod in oblivion...

Can you script companions? If so, it might be worth having a something to permanently summon daedra/undead to guard your tower/follow you...

You might also want to create a compatibility mod for Morrowind Comes Alive, or you may get people spawning in funny places... The simplest way to do this would be to disable MCA for the area, but you could cause NPCs to spawn in bars and shops...