10 of each glofish will work.
How rounded is the gravel? The majority of bottom dwelling fish don't have scales so they need a soft or rounded substrate.
Skip the discus, they need higher temperatures and are delicate.
Guppies may or may not get nipped because of their tails.
I know rasboras and platys are peaceful fish so adding either would work. The platys I have will scavenge for food on the bottom of the tank and eat some algae.