Hi Hanyo!
I would suggest fire up a copy of tbaMUD as your base, and get stuck into building out your world.
Almost anything you need can be achieved using triggers, and the bits that can't - well you can post request on the forums and are bound to get a response.
If you run with the CircleMUD releases like CWG/Budda you may run into bugs which have been addressed already by tbaMUD. Balance that against how much you want the features they include.
You'll find patches for classes/races/skill etc for tbaMUD which cover a lot of what CWG offer. But changing tbaMUD to a pure D20 ruleset is a lot of work, and not worth the effort if you ask me. Although pure D20 rules don't lend themselves to computer gaming in my opinion anyway
Whatever you choose
Good luck!