Rummynose tetras are great schoolers. They school alot tighter than my other tetras and I only have 4 of them. A bigger school would look great. They would also stick together more with some bigger fish, like angels, in the tank.
Dwarf neon rainbowfish (Melanotaenia praecox) are a smaller type of rainbow that are still very colorful. You could have a school of them, as well as some Rummynose, along with the angels. If you go for a larger type (Bosemani or Turquoise) that get around 4 inches, I'd substitute them for either the angels or a school of fish. Basically what I mean is if you get a school of the larger rainbows, you could either have a 2nd school of fish with them, or the pair of angels...along with some bottom fish.
For mating habits, you could get some Rams. If you get a pair or 2, you could end up with some eggs and maybe even fry. If you leave the fry in the tank, they will probably get eaten (if they don't eat the eggs), so you won't have to "deal" with them, unless you want to.
German Blue Rams or
Bolivian Rams will work. Germans are obviously more colorful, but they can be sensitive to water quality, so add them long after the tank has cycled, if you go with them.
The bigger fish you could get would be angels. They get around 6-7 inches tall and about 5-6 inches long.
You could get a pleco for the bottom. Bristlenose, rubbernose, and clown plecos are all good choices. Or you could get a fancy pleco if you want to order it offline.