My suggestion is slightly different from those given because of the trees your working with. All of these are great ideas that are given above but to add to those i would suggest
#1 do a test crop now with a small number of trees (5 or less) What if your soil can support pawpaw fine now?
#2 Do a soil test and find out what your soil has or is missing
#3 hire or rent a tractor with a roto tiller now if you can afford to wait 3 years to plant till the organic material to the bottom now which will lock up nitrogen temporarily. Chopping up the clay and loam and mixing it with lots of wood chips and manure would bring the worms then you could cover the entire thing with wood chips again.
#4 if you cant wait avoid tilling in the chips and instead pull back the chips and work manure in about a 6 foot area where the tree will be planted.
#5 pawpaw as babys hate sunlight be sure you are ready to shade them
#6 They like organic material in their soil be ready to meet those needs
#7 They like water we prepared to water them
#8 Do not grow them in pots as long as you plan unless they are grown from seed now. Be mindful the roots are not rootbound if you do.
Pawpaw roots are super sensitive so damaging roots can be a death sentence.
Pawpaw are not as easy to grow as everyone says if you have a vacant field that nothing has grown on in awhile. Try to watch the following video on pawpaws needs hes right
Here is a thread on how i do it but its a little harder in Kansas than 90% of places out there but it can still be done Pawpaw in Kansas - it's a lot of work but can be done!
I’ve learned what works in my area may not work in yours so look at yours only for final advice.