I have 10 rats, 5 gerbils and so many hamsters, it really depends how much time you have to devote to them. I sometimes take in rescues, i do admit pairs of dwarfs are easier to look after as they can entertain themselves and you can get away with only holding them occasionally to keep them tame but the more attention they have the better.
The rats get to free range in my room at night after their tea boys and girls seperately though
wouldn't want any accidents i really do love my animals i think they are probably better fed and in better health than me