1) The water of an aquarium doesn't have much beneficial bacteria in it. Gravel and filter media do. I wouldn't call your tank cycled, until the sand was just in another mature tank...you didn't quite make that clearSo, I bought a Mexican Dwarf Crawfish for my 30g work in progress tank today.
Its cycling with my two cichlids, two danios, and a clown pleco in it (doesn't really need cycling - I used old sand and put in about 5 gallons of established aquarium water in it, along with some quick start stuff - I'm just saving up for the remaining work on it)
I wanted a pretty red crustacean that was large enough my cichlids wouldn't bother it.
Does anyone have any experience with them?
2) What kind of cichilds? Africans will bother/fight everything, and some SA cichilds aren't much better...Rams, kribs, and angels are another story.