I'd say it's fine for one.
They grow very slowly.. and I think 3" is the max.
They prefer sand, mine likes to bury himself from time to time and they come out a lot more in low light. They aren't very active, because... well you'll see when you get him, they drag their bodies in a really awkward way that probably tires them out.
If you have gravel, that's fine, but sometimes they climb up the glass and fall, this can break the shell, but it's fine and grows back. Note, I have seen mine on the glass once in the 2 weeks I've had him.
They are often called heavy plant eaters... I've pulled mine off the crypts twice, but if you feed him with something else it'll prevent him from eating the plants. Just put the food in and put him on top, mine would eat all through the night.
I'd feed half a cucumber slice every other day.. though now I have bottom feeder tablets for him, which is also good, and more nutritious so I'd recommend it in the long run.
They also need calcium for their shells, either plain cuttle bone that you can find in the bird section, or spinach leaves are two good starting points.
I leave in veggies overnight, since that's when he does most of his eating, and remove in the morning, unless he's still eating.
Also, they need a pH of at least 7 or more.
Curious, how much do they sell for where you are? I paid $6.50 for mine, and so want to take great care for it.