5.5gal start out with 4 Multi's, sponge filter, lightly dust the bottom with sand, do about 8 whale eye shells, frequent water changes should be fine..
I know you said that the fry is an issue but your not going to be able to tell the sex when you get these guys small, so your only option is to find a breeder and get all males or wait till the they are bigger, Multi's when full grown males will be twice the size of females..
As for anything else Brevis and any other Shell Dweller even a 10gal will be too small so i would say stick with the Multi's..
I know you said that the fry is an issue but your not going to be able to tell the sex when you get these guys small, so your only option is to find a breeder and get all males or wait till the they are bigger, Multi's when full grown males will be twice the size of females..
As for anything else Brevis and any other Shell Dweller even a 10gal will be too small so i would say stick with the Multi's..