What your building is a cold water tank. Paradise fish would fit but may eat the minnows. Most of your centerpiece fish for a cold water set up may eat the minnows. May want to look into another school and forget the centerpiece.
How big of a tank are you thinking?
Have you considered sunfish? There are dwarf sunfish that only get to 1-2 inches long.
I can't speak on how that work work as I've got no experience with them.
But may I make a suggestion on the tank size? As someone who had a 55 gallon for years before upgrading to a 75 (now a 90), I would suggest starting at the 75 size. The added depth is quite helpful in stocking and scaping the tank. Plus it opens up a whole new can of worms in what size of fish/how large a school you can keep.