Mrs Trip and I spent a couple of weeks in the Big Bend area 2 years ago this month. Had a great time, and you will too. Here's a thread about our ride down to Peguis Canyon and a few shots of Big Bend.
You can get a lot of information right from the Park HQ which you will pass on your way to Rio Grande Campground. When we were there it wasn't crowded so we moved around to different campgrounds, including in Terlingua. You can get a National Geographic map of Big Bend, and the park has 2 small booklets, "Road Guide" one to paved and improved roads, and one to backcountry dirt roads. No off road riding in Big Bend, but some of the roads are a real challenge. A couple of the photos I posted are on Old Ore Road that starts near your campground.