Well, I can tell you that they make fantastic appetizers! But that's probably not what you're looking for, right?
Thai crabs (now mainly called red claw crabs) are fiesty little guys. The males tend to be a bit nastier than the females. You can put half a dozen or so in a ten gallon, but I wouldn't go much above that, and make sure you have good filtration as they are huge waste producers.
You can use any type of substrate, but think about a couple things. First, the crabs are dark, so you'd want to go with a lighter substrate to make them show up best in the tank. Unfortunately, due to the massive waste, going too light is going to really make that poop pop in your photos! I'd definitely go with sand. The waste stays on top and makes it much easier to clean out with a siphon. Pool filter sand is great because it's heavier, inexpensive, and stays put. You'll want to stir it up slightly during mainentance to avoid anaerobic pockets from forming below the water level, but that just takes a second.
The crabs will eat anything you toss in there, including other fish. If you decide to add fish to the tank, make sure it's a type that swims in the upper region of the tank, not bottom or even mid-level fish as they will definitely become snacks during the night.
I'm going to just assume you know about the nitrogen cycle that needs to be done prior to setting up a water tank, but if you don't feel free to PM me and I can direct you to some easy to understand links. It's not as difficult as some make it sound.
Good luck if you decide to get some. They're very interesting little creatures. Beware, though. They pack a heck of a pinch!
*edit* One thing I forgot. They do better in hard water to keep their shells healthy. If your water is soft, add some crushed coral to your filter housing to increase it. Feeding high calcium foods also help. Blueberries are a great treat and have lots of calcium as well.