I'd take the bike to a shop to get fitted first. It's amazing how much difference that makes as far as comfort goes. My second suggestion is to start with the easy trails, Houston has several, and build your skills and confidence.

That's my .02 as a total newbie. My partner jumped in with both feet and has far exceeded me with skills, but she's also far exceeded me with injuries. My personal motto is slow and sure wins the race.

Now the people who actually know something can offer better advice