Since platys stay relativelt small ( ~ 2.5 inches ), would a trio of females be compatible with some of the smaller fish like Flame Tetra, Lemon Tetra, Glowlight Tetra and Harlequin Rasbora?
They'll get along pretty well with other fish, however the other fish may not get along so well with them. Some fish can nip at them, and such. As long as you keep the Tetras in decent-sized schools, you should be fine.