I don't think you'll find an open world game with everything you want.... I mean think about the computations needed to be processing a single or multiple ai's to persistently construct buildings, run an economy go out and adventure, gather xp etc and manage all their units. It's not like a game such as (TOS) Oblivion where the enemy don't really need their ai to kick in until you've begun to get close to them and they only need some simple routines; they'd have to be active all the time in this free roaming world.

It's something to look forward to in the future but I doubt it's managable at this stage :) (maybe if the game was turn based ala civ/heroes of Might & Magic but not real-time)

Thank you all for your advice and help! I have actually found two that have roughly what I'm looking for, X3: Reunion and Evochron Mercenary, although both are space flight games instead of RPG's. Again, I do appreciate it.