Loving this thread! A good idea source you may want to take a peek at is Floret flowers- they put together seed collections in all sorts of color ways that may inspire some of your choices. Here's one based on your idea for using zinnias but do look at her others-
https://shop.floretflowers.com/colle...ion-fiesta-mix
I grew basil aromata last year as a pretty and nice smelling filler- herbs as fillers add a whole new dimension to me and I think that might translate at market well.