I haven't thinned. Haven't felt the need. My two trees are well into mature production. I overheard a portion of a discussion regarding pawpaw thinning, back when the HOS presented the summer open house and was hosting the NAFEX annual gathering, folks in attendance included Ron Powell then president of the Ohio and North American pawpaw growers association and a grower from Pennsylvania  I met while looking at the HOS pawpaws. Anyway that part of the discussion was short, focused on a reason for fruit thinning as remedy from over burdened branches breaking. I haven't experienced that , and don't have any of the touted larger fruited varieties, so that didn't seem pertinent to me.     I would suppose that thinning fruit when they're small might increase the size of those that remain, but I think a pointless exercise, except as for above. My observation is that fruit sizes are all over the map. You will find a single fruit or double cluster or even three that are moderate in relative size, or a single that is smaller or larger. Clusters of 4, 5, or even 6 not uncommonly with similar sizing, all large or moderate, or mixed sizing within the bunch including 4 larger and a moderate or two and/or a smallish. For the most part the smallish ones are often as good tasting as the larger. Maybe not as satisfying as a whole handful but if it's ready, in hand, or introduction to a sceptic. As they say "that's some mighty good eatin'. If you're looking to market then I'd just select what you're showing.

In regards to hand pollination. After three years of very successful hand pollination, two years of abject failure prior, and 2-5 years hoping previously, including painting fish fertilizer emulsion on plant crotches neat flowers-nada....- the pollinators finally showed up. I noticed fruit in areas I was certain I had not visited with my pollen transfer efforts. I determined to see what would happen from that point on with the natural pollinators and set aside my brush. Fruit production dropped to maybe 30-40% that first year. 40-60% the next, and it's been very near that of the hand work, for the last couple of years. Although my shy one seems to fluctuate a little but seems on track with the growth and continual more blossoms resulting from the growth.  

I haven't really pruned much either, except when a limb is in my way. A catalog listing mentioned a pawpaw that took well to pruning. I don't recall what catalog or which Pawpaw. From time to time I will cut back a limb that's likely to reach out too far into the raspberries or droop to low to where it's subject to inadvertently getting fruit knocked off as I or someone else pass by. I suppose I could beneficially prune out some too closely spaced redundant lateral sticks/limbs and cut back some well placed others to encourage new growth on the interior there.