As far as the burring in the sand goes it is a defense mechanism when they are small. like the softys they make a good snack at that small size so nothing to worry about they do it when their bigger too but its for hunting more then defense and as far as putting it outside if you do for the summer I wouldn't put it outside until it has at least an 18inch carapace at that size his bite would brake a raccoons arm
and any bigger he might eat one. If they didn't eat fish I would use them as guard dogs for my koi pond lol