Adding texture to the
land, like mounds and low spots will help create diverse niches.
Put some rock piles in for heat retention and insect predator habitat.
With that clay, I would try to make a small
pond, or infiltration basin, with no liner, to increase diversity. (put some fishes in there if you can seal it to eat the mosquitoes if you have any skeeters in your area).
I would plant a bunch of
root vegetables: daikon, radish, turnips, carrots, beets to help break up your soil. Then leave them to rot, nevermind the smell, it will leave tons of
carbon pathways for your plant
roots.
I might also take a broad fork to it to get more air into the soil.
Some small swales 1' or 2' wide, filled with gravel if you don't want it to look weird or think folks might trip.
As for planting polyculture, I mix the small seed with other small seed and big seed with other big seed. At the end I have 2 mixtures: big seed and small seed. I would make the mix mostly biennials and perrennials, or annuals that perrenialize in your area.
Trees, might think about a couple of those.
Comfrey, great mulch source.
Fling away, kick or rake dirt over the top so the birds and
mice don't take all.
See what does well where, watch things grow and interact.
Capture as much
water as you can.