Emerald crabs are pretty pointless, IMO. They are rarely seen, and will become predatory once they become fully grown. People say they eat bubble algae, but mine never did. Actually, all crabs are predatory to some extent, they are opportunist. So any bottom dwelling fish like a Goby might end up getting eaten if its a tiny one. Snails will be predated on as well.
If you want starfish, I recommend mini brittle starfish. They basically eat crap and will multiply in your aquarium. Chocolate chip starfish eat algae and can be added to a fowlr. Just read up on what starfish you pick, as some are will bury in the sand bed and die off, and nuke your tank if it cant handle it.
Clarkis are nice clowns.
Liveaquaria.com is a good reference site to see what is compatible with other fish and what it needs are far as aquarium size.
