In their first few years of life, pawpaws typically do better with at least partial shade. I have my babies either under a willow tree to nurse them along (I plan to significantly trim said willow later on once the pawpaws are established) or I have a shade cloth over top of them which I move higher as needed.
If your trees are already 4 ft tall, you might only need to shade them the first year as long as they become established. I’d suggest fairly regular watering and a bit of high nitrogen fertilizer starting next year. Make sure you keep the area around them mulched and devoid of grass if possible, but keep the mulch from directly touching the trunk of the tree to avoid any rot issues.
Are your trees a particular cultivar or are they seedlings?
seedlings - i think i will need to craft once they are fully established
at this point i am considering keeping them in the pot they are in and overwinter them so that in the spring i plant them out - what do you think of that?
If the pot is a tall one, you could try that. If you know exactly where you want to put them, though, that is usually the best option as long as you can keep up with watering them to help the roots develop.
If you plan to graft, you really only need to worry about the roots anyway, rather than keeping the leaves happy.
It is usually recommended to plant pawpaws in the spring rather than the fall, but it can be done with the proper care. If you can overwinter them in a tall pot (14+ inches), a 5 gallon bucket or something similar that might be a good option too.
You might ask the nursery if they were growing in full sun before you bought them,if the leaves are not sunburned, try to be consistent with what the nursery did in terms of shade. Then when you do plant them, if they are not already sun tolerant, construct a partial shade to give them only about 6 hours of morning sun only for the first year, then they should be ready for full sun the next year.