1) It's been years since I did any work with film, so I'm afraid I can't help you there. I've just got a DSLR that I use now.
2) ~20 seconds. If you go very far beyond that, you'll end up with trails instead of nice clear shots. 30 seconds is passable, you'll just end up with tiny, tiny trails - probably not that noticeable unless you look closely. You may be able to stretch that out a bit more if you have near-superhuman vision, a geared tripod, and a steady hand, but I wouldn't count on it. That's not a bad thing though, there are some great images done that show the movement of the stars. Not every picture has to be tracked in order to be worthwhile.
3) Personal preference. I've taken some pictures at 18mm that I loved, and some at 200mm that made me just as happy. Experiment, and see what turns out catching your eye. Everyone has a different sense of aesthetics. What works for me may not work for you.
For any pictures you do take, I highly recommend the Astrometry group on Flikr
. It's a bot that will match up your images with a massive database covering the night sky, and tag major features in your images for you. I certainly don't know everything in the sky I'm looking at when I decide to take a picture, so being able to upload it and have all the major features identified is incredible. In my experience, the people behind it are great as well, and very willing to share the datasets they use.
That said, if you want to get serious about it, you should look at picking up an equatorial mount. It's high on my list, right after a nice intervalometer.