Try to find the best/healthiest looking stock/fish you can. Add them to your tank in groups of 6-10 at a time. eg. 6 one week, then 8 a week later.
There are quite a few fish that work well with them, but also quite a few that don't work.
Livebearer fish eg. platies, swordtails, guppies etc.
Bottom dwellers eg. corydoras catfish, bristlenose, loaches etc.
Dwarf cichlids eg. bolivian ram, blue ram, keyhole cichlid, apistogramma etc.
Other small shoaling fish eg. barbs, danios, rasbora, other tetras etc.
The above work fine with neons. The below not so well.
Angelfish, will eat them once they mature/grow to about 8-10cm. And they will continue to grow to 12-18cm.
Larger cichlids (angelfish is a cichild too).
Black ghost knife fish.
Pretty much anything that can fit them in their mouth and match/best their speed.
Siamese fighting fish/betta splendens. Not advised. Sometimes the betta will take them on, either whenever he feels like, or if he can't catch them, then when they sleep. Or the neons may nip the bettas fins stressing it out.
I'd suggest some platies and corys for the tank without knowing the dimensions.
2-3x platy
4-6x cory (all same species preferably)
6+ neon
would look nice.