That looks like a big piece of work. We did something similar on a smaller scale in the bed where bamboo had been growing:

After all the roots had been axed out, there was a shallow depression which we filled with trimmings from the tomato plants and other vegetation, and then covered over with finest homemade compost:

The surrounding ground is very hard, but come the autumn when it gets wet, we'll fork it over and mix everything up a little.
I don't think we have enough food waste for bookashi, mainly fruit and vegetable scraps and eggshells. And teabags 😍. Everything else gets eaten.