Ive got a Sesarma bidens (Red claw crab)
Diffrent from your's but ill share what ive learned.
He's blind as a bat as they say. hunts by movement and scent.
Started as a algae eater but cleaned it up rather quickly. Currently he eats shrimp pellets. which he seems to like.
When it come to tank size id say depth is'nt really an issue, actual ground space is whats improtant.
He's a messy little bugger makes hes tank filthy. even with once a week vacuming.