Which Shadowrun Edition to Start?
Fourth edition has a lot of supplemental material, with nearly everything you can think of covered in one book or another. Fifth edition is rapidly catching up, though, and they're making sure to cover high-priority options quickly. (Older versions got a reputation for treating riggers as a lesser option.)
If you don't want to worry about new material turning up and throwing a wrench into your game, go with v4, because you can then pick which books suit your game and leave it at that. You could even just play "Core Rules Only" and be just fine.
Whichever edition you pick, I'd recommend staying away from the official forums until you've had a chance to play the game yourself for a while, and have a hang of the rules. The people there can be very helpful when it comes to answering questions -- you won't get called a noob for asking for basic advice -- but they can really over-analyze a problem.
Granted, once you've gotten familiar with the rules, the official forum is a treasure trove of house rules, new material, and advice. They have people playing every edition, even the first. (Back when "rocker" was a valid archetype, if that helps set the date.)