Like several have said above, get something with tracks and a blade or good grapple/bucket and make piles.
I think there is room to disagree, but, I would try and get all the brush, junk, and even some top soil, kind of scorched earth. then put it back how you want it, without worrying about running over nails, rebar, etc.
If you do it with an x, and the conditions could work, just burying all of it, isn't all that bad if not in a wet land, or near a water table.
Good luck!! I have done some of this, and where I am, unfortunately the best course has been scrape and load a dump trailer, and haul it off, time consuming, but, it is all gone.
Best,
ed