Well as for plants as I was thinking along the lines of Indian fern, Amazon sword plant ,moneywort. And sorry for my miss spelling so if I just had guppys I read that you can have 10-15 guppies per 10 gallons??
Am I going the right way with guppys??
I have Amazon swords and Indian Fern (presumably this is Water Sprite, Ceratopteris cornuta, a superb floating plant). With the T5 lighting you will have algae issues.
If you have livebearers (guppies, etc) you will probably only want males, otherwise you will have dozens of fry every month once things get going. I would find guppies only in this sized tank a bit drab, but then I am not fond of guppies. The rainbows would be beautiful.