On my game (which died a quick death, but made a great demo for Ensemble), it was a lot of self-taught stuff. But, the basics of what I knew came a lot from the college classes. Everyone has their own story; there's no single, definitive right thing to do. Pick something that works for you. If you find you don't have the energy to finish it, then I think you owe it to yourself to ask yourself if you should be doing something else...
On our artists, they come from all around. Art Institutes, Sheridan College in Canada, and a ton from various game companies.
Designers have probably one of the toughest jobs to interview for... Short of tons of design materials, how do you show yourself to be a good designer? Thus, most designers end up starting in content design/level building, as that's an easier thing to demonstrate and is the 'general' entry level design job. There's a billion games to heavily mod to show off your design skills, so that's a good place to start. To be a designer at Ensemble, you've got to be able to do paper/top-down design, too. The "So, what was wrong with AOM?" question comes in handy here, toodave