Actually just a front brake should do you just fine. I have front and rear brakes on my road bike, but I NEVER use the rear brake. EVER. In fact, I think I'm going to take it off. Since you sound like you are new to bikes, I would take it easy on the braking if you do decide to just run a front brake, at least at first. You definitely don't need a rear brake, but just be careful for your first few rides to not lean forward too much. Also, I can't tell what damage has been done to the bike or how the paint looks really, but it does look like a pretty good deal. Worst comes to worst, you replace the rear hub which isn't too expensive but you would have to pay a shop for the labor most likely.