yes, but not for the fish and crab hitting one side.
5 clowns is too many for even your tank. They will grow up and eventually there will be a dominant female, a dominant male and the rest will be chased around and beat up. Not pretty. You may get lucky and they will be fine, but don't bet on it.
Also, horseshoe crabs are not good for tanks. they get big fast (like over a foot in length) and will quickly starve in a tank. This is one of those creatures best left for very large public aquariums and the ocean. If you can, take it back.