Ummm well there you go, you have a 10g so why are we wasting our time discussing the 5g.
Fishman, i like you. I like your enthusiasm, but you are always so ready to jump head first into a mess of a tank. Yes you could keep a few shellies in a 5g but given your history (and anyone here who has been around a while knows your history) its going to turn out as a disaster in a 5g.. Im not being mean just constructive. (I may be mom'ing you a bit)
If you want I wont give you advice, but I bet any of the others would have the same thoughts.
I REALLY think that to do shellies right you need a 30g long. or at the very least a 20 breeder.
All Glass Aquarium AG 20L Tank Black 30x12x12
like that one that sells for 38 dollars. It gives you 30" of floor space and would be a really nice home for shellies. that size tank would need a water change of 5 gallons (2 small buckets) a week, so it should be easy to keep up with.
There is something to be said for DOING IT RIGHT THE FIRST TIME