What a great project! And lucky the airport says OK.
Your goal is.. mix of showy flowers all summer and fall? support insects and be native plants? You chose wildflower mix because it should be self perpetuating and full of flowers?
Black eyed susans should colonize
wild milkweed, collect seeds in fall and throw them there.
Pycnanthemum aka mountain mint is a hands down winner in our native garden at work. Insanely loved by huge variety of insects when it is in bloom. If you find plants to buy, they will spread very well. It won't look flowery and showy, though.
Cosmos, the purple pink tall ones, I thought they would self sow but apparently they can't compete. My problem with cosmos is how late they are giving any flowers.
Yarrow, if happy will spread.
Ditch lilies, not my choice but will last forever, bloom in July, be showy.
It does look like purslane is a lot of that. With no help, you'll have a lot of weedy unflowery stuff. Yes, wild evening primrose which is OK to me, it blooms, is native, will colonize and compete.. I think I see orange wallflower which I think is not native to the area.
If you think about it, if fields full of flowers all summer was a naturally occurring thing, then.. they would occur, but they don't.
But I have learned at work that a few bright flowers will make up for a good amount of weeds. Maybe you can plant starter plants, surround each with grass mulch, hope they spread over time. Learn about your volunteers, you may want to keep some (mullein, late flowering boneset are two more that I'd expect)
