Pistol shrimp and wathman goby...

Hello, I am changing one of my freshwater tanks to saltwater, I have a 75g now.. a friend of mine suggested, because of the size, to put in a sand bed, and then put in a pistol shrimp, and a yellow goby.
I went to several online stores and found several different types of pistol shrimp, and several different types of watchman gobies, what, in everyones opinions, are the brightest most colorful species that I can put together??? Also, what else would go good in this tank?? This tank is 30g so I don't want to overload it, I am talking about additional items such as sponges, corals, invertebrates, etc...... have ability to put in metal halide lighting as well... if I could put in some clams or something..
Also, does anybody have a source for clams to use in a refugiem?? to use as cleaners, looking to get 20+ clams, not sure what types are best for this?

 

This is a nice one http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=2112 and a shrimp that could work is http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=702 im pretty sure thes guys can go together but im not sure... the goby looks nice though and for the clams...uh do u mean giant clams like maxima and crocea cuz i dont think those can go into a refugiem because they need high intensity lights and don really know how much they clean...