Thanks everyone. Did my trial run yesterday. It's not a bad little ride. I'll definitely be riding some unlit trails, so I'll need a good light. Apparently chain guards are a rarity except on fixed gear bikes, so velcro strap it is. Aside from a baffling spot where a trail crosses a major street with no stoplight, crosswalk, break in the curb, or even a gap in the median, it looks pretty straightforward.
Since my current bicycle gear is comprised of a helmet, I guess I'll need bicycle shorts, reflective vest, leg strap, head and tail lamps, portable pump, patch kit, and spare tube. And probably eventually some cold weather gloves. I've got plenty of stuff for layering - jackets, long johns, etc. Anything I'm missing?
I'll probably be borrowing my girlfriend's mountain bike until I'm sure I'll be doing this for the long haul. Don't want to drop the cash for a bike and then stop after a week or two.