I'd say get what you want within reason - like if you only wanted to get 1 lone bantam chick and expect to safely integrate it with the rest, that could be tough. Or if you already have bullying problems, adding more birds could make it even worse. But if you get a mix of chicks and integrate them as a group, really shouldn't matter if you get 2 of each breed or singles or a whole group of just one breed.
Personally I like having a diverse group, so I get 1 of each breed I'm interested in with exception of Easter Eggers since I enjoy them. So currently have 2 of those, might end up with 3 soon, who knows.