That's exactly why I bought a Sector 9 board a few years back. I love it. It's great for helping switch riding and bombing hills makes me happy. I'ts one of the longer boards, 48" inches I think, with very little concave. With your size and what your looking to do, I would go with around 44" or longer. Especially if you have never skated before.
The selection in Dallas sucks, I would suggest you go to one of the skate parks in the area, either X-games skate park in Grapevine Mills Mall, or Eisenbergs up in Plano. They should have at least 2 or 3 longboards you can look at to size them up. If you don't see what you like then order online... Check these out... www.sector9.com www.gravityboard.com