Whilst filming many bits of paintball over the past year, I've taken several direct hits to lenses, bodies, etc. I've only had to disassemble and service the camera twice - both times because I had been mugged in the focus ring.
As far as filming/taking pictures in the woods - the best way I've found to do it is to actually play with a camera. Go in, run, shout, etc - instead of shooting paint, you shoot pictures. It's really good fun, plus it's a great alternative if you're running a tad low on paint - keep playing, but you don't use any paint! See if you can get a really fast AF lens. The GH3 50-200 has probably the fastest autofocus you'll see on an affordable lens/set-up. Plus, it kinda looks like a blunderbuss.
Tourney - be prepared for pain. To get good shots, you'll need to stand fairly close to where the paint is flying. Paintballs, as we all know, aren't exactly renowned for accuracy. You will get hit. Your camera will be at-risk a good 70% of the time. If you're just taking pictures - the best thing I've found (I have yet to test it chompreshensively, but I'm making a video on that soon-ish) is to wrap the camera body in cling-film. Your camera will typically hold up to a few shots to the body. Worst I've ever - and I mean ever - had was where a paintball bounced off the side of the lens and knocked the mount itself (was an MFT mount though.) a tiny bit out of alignment. Clicked it back into place and boom, good to go.
One of the huge Eclipse/Exalt/Whoeveritisnow microfibers with a caribener on it is probably your best investment. I can't count how much footage I've scrapped because of a bit of paint that looked like I'd wiped it off properly, but on closer inspection, found it had smudged it.
Good luck!