Yes, flowers would be beautiful. Red, white and Blue to go with your patriotic bunting in the window.
I would do Red Begonias, White Petunias, and Blue Salvia. Those I would put just up on the bank. In the drainage ditch I would put Elephant Ears or Fountain Grass or maybe both. They will be big by the end of this year and they will add texture, form, and movement.
It's too bad you don't know someone who could dig you up some plants to share because that looks like a big enough area to hurt your coin stash. If you have gardening friends I would def hit them up for a handout.
