Fall planting, or seeding? Either way, I would suggest for tall grasses to go very sparingly on the switchgrass, a bit stingy on the big bluestem, and go stronger on the indian grass and the little bluestem. Switch and big blue have been very aggressive for me, and will catch up no matter how little you start with ion proportion to the others.Pale, purple, and yellow coneflower will not take as long as some other plants to establish themselves, and cover blooms from late spring through fall. New England aster and brown eyed susans also establish and spread aggressively, and give a great fall show. Butterfly weed is al it is advertised to be in beauty, hardiness, and fodder for butterflies in all stages. Purple prairie clover doesn't bloom very long for me, but is very pretty, and the birds ffed on the seedheads all winter, and it is supposed to act as a natural fertilizer. Hope this helps; I am just a hobbyist, but these have been the results of several years of experimenting in my back yard.

good advice from fiddler -

before i can offer any suggestions its probably best to know the soil, light and moisture condition of your area...
dry and sandy, moist and clayey or somewhere in between?