Would this fish tank be overcrowded?

If people have issues with your setup with Rosy Barbs, substitute them out for the Cherry Barbs. IMO, they are a more vibrant attractive species with a deep red coloration in the males and a yellowish hue in the females. They max out at about 2" (smaller than the Rosies) so you'll be good with a small school of them. I have them and they are quite active and peaceful (being housed with Cardinals, Oto's, and a Ram).