African Dwarf Frogs-A good little creature to have because they are cute IMO. They do great with mild tempered Bettas and Community fish.
Bettas-You can go one route with a male Betta as your centerpiece or can get three or 4 (very peaceful) female bettas of different color. Go the male approach you can add some tetras and perhaps an Oto(or 2) or a couple of ADF's.
Bue Gouramis-IMO get to large for a 10g. If you keep up on your wc's maybe 1 with a couple of Otos or small catfish, Corys perhaps.
Crayfish-Will do fine with fish for a while but never put with another cray or with bottomfeeders.
German Blue Rams-Sensitive but if you keep up with wc's you can get away with a breeding pair IMO. When they breed they are aggresive and other fish will probably get killed.
Killifish-Good jumpers. Keep a sealed lid. I say maybe 3 Threadfins or a Threadfin and some Tetras.
i like the idea of female bettas, what kinda tank mates would be good with 4 females?
and also i like the idea of the german blue ram i only seen one at my lps, would it be safe to keep one by it's self if so what kinda tank mates could it have?
they will be safe in the tank by itself but not for others.It will turn more picky to other fish.I woud recommand you to do it with betta or plakat,now plakat are quite famous,they come in many colours and they are way more active than betta.
With 4 female bettas in a 10g, you would only have room for a few little bottom dwellers. I've personally had bad luck putting 3 female bettas in a 10g, I think it's just big enough for one territory but not big enough for 3 or 4... you might be able to do 4 if they just decide it's too crowded and there aren't any territories.