Unfortunately killifish are rarely seen in the lfs. They have a reputation for being short lived and difficult to keep.
There are so many species that it's difficult to put them into a single niche.
Most killifish keepers will have them in separate species tanks so the offspring can be traced back to an original line or collection point.
As well as having a number (large) of individual species tanks I have a 350l house tank with some pairs and some males or females of a number of different killifish of mainly Aphyosemion species along with poropanchax Normanii . These work with the two species of corys and odd Emperor tetras to give a very active environment with anything that can find a mate producing eggs which sometimes make it through to maturity. Mind you, my tank is very overgrown so there are many places to hide.
It depends what you want to do with the tank, do you just want to have a few killifish alongside other species for decoration? Would you just want males for display or breeding pairs to keep the line going .
If you have any questions about killifish let me know either here or by pm. If i can help in any way,
Cheers
John