give yourself a time limit for each fortress so you keep on track.. it can be easy to fall in love with a particular embark and end up never filling out your world. this is coming from someone who has shared a similar dream to your own but never quite sticks to the idea.
This would solve two problems I have with pre-generated worlds with long histories. The pre-generated structures have no design and are merely complex mazes, and I can never get a full understanding of the history.
well stated, I agree with these assessments. in many ways DF reminds me of Elder Scrolls II in the way dungeons and caves are utter chaos..
another tip, review your world with legendsbrowser or some such utility and get an idea of the civilizations. you may have generated a fairly uninteresting world or a world missing certain races, that sort of thing. good to confirm it's perfect before you commit to building.