All of this sounds good exept I'll correct just a couple of generalizations.
Best to provide around 2 shells per shellie
Some shellies, like brevis, can actually go with just one shell for a pair of fish, while other fish like Multifasciatus in fact prefer large amounts of shells, and I recommend at least 5 to 10 per fish. If you are short on shells they cluster them together like this:
This is the handiwork of the fish, I didn't touch a shell.
They live in half buried shells
You can see how Multifasciatus actually clears the sand from around the shells in the above pictures. Some types will choose a shell and bury it completely except for the opening.
Any kind of shells work. I go through my lfs's apple snail tank and take the empty shells from it You can use escargot, and you can order authentic Neothauma shells online if you are really into the biotope thing. Whatever you use, boil them first.
They work well in small tanks, but my favourate way to keep them is in a community, where there are other fish in the tank that they need to defend their territory against, it's fun to watch how aggressive these tiny guys are. This is a 1/2" female keeping an eye on a bristlenose that is feeding a little too close for her comfort. They stand their ground even against much bigger fish, and seem to be able to distinguish a trespasser from a predator.
Shelldwellers are fish that while short on size and color, is quite full of character and energy. They are easy to keep as long as the water is clean. Make sure the tank they are going into is cycled, as they tend to be sensitive to ammonia. Sand is most certainly best because they love to dig.
Every species is different, and not all of them will do well in pairs. Some are best in harems, and others are best in a colony. Because they are as territorial as already mentioned I don't recommend them in anything less then a 30" long tank if you want other tankmates with them.
/www.cichlidae.com/articles/a061.html
