Any plant you put in should been kept in your home for several moths prior to being used as crabs are very sensitive to any quemicals they may contain. Your terrarium is on the simple side which may turn tricky. A larger one with deep peat for burrowing and a salt and fresh water containers would be better for long turn sucess. Keep the water changes up, this guys foul their water easily and they are very intolerant of amonia. Actually the water containers should be cycled like a fish tank, otherwise its harder to keep them in good shape.