I really managed to start some paw paws from seed! But are they variable from seed? How many should I plant to get some good ones? What do they like soil sun etc.?

There will be all kinds of variety when grown from seed, I would plant as many as you can. First two summers they should be grown with ample shade and wind protection. Mature trees, however, do best in full sun but oo much dry wind will damage their leaves at any age. Some acidity in the soil is a plus.

Its best to plant as many as you can, when your trees start fruiting you will see are fruits from your trees are good enough for you and if not you can try grafting over that trees with scion wood from tree that is good for you.

Here are two of mine videos about grafting pawpaw (so you can see how to graft pawpaws).