You can keep it in a pot, it doesn't matter if the water is deeper or shallower, it won't drown it. But it's best if the water is just soaked through the shell. You can let it bask in the sun, not too long. The water can be used tap water, but only after a day in the sun.

Crabs are omnivorous.

You can feed them fish ah, whether raw or dried fish, they can accept. You may also feed them fish feed, red worms, shrimp, snails, mussels. It's best to feed them some grasses regularly, with bitterweed, ilex algae, and so on. As long as the feeding is ok,you don't need to worry about the rest. Crabs are very good to keep.

But you have to take care of it carefully because it's injured and fragile. As long as you take good care of it, after a few molts, the feet can grow back.