You will need to look at the Kanza variety which is a cold hardy. There may be other varieties that do well, but Kanza is the go to for the northern plains states for pecans. Cape Fear, Elliott and Desirable may also be varieties to research; but I don't know your climate.
You will definitely need a type I and type II variety in the same vicinity. Kanza is a type II. Pawnee is reported to be a good pollinator. The male and female parts of the pecan trees are present at different times of the season, so they won't self pollinate. One has to have another tree that will provide pollen at the same time the tree is receptive to pollen to produce fruit. Planting multiple varieties may increase your chances, but with wind pollination it is more about the correct timing and distance than diversity.
I have used these folks with good results:
Texas Pecan Womack is a highly regarded supplier, but their prices when way up two season's ago.
Womack's
You will need to plant bare root stock around the March time frame. I plant in late January or February, but I don't have hard freezes as you may. Tip: don't let the
roots begin to dry. Keep them damp at all times. That means wet burlap even when you are in the field planting. This also means short shipping times are better. Depending on the orchard lay out you select, you will plant 12 to 24 trees per acre. 20 acres is a lot of trees. I find it more economical to go pick up my trees in a trailer, so I can ensure they are kept moist and protected. If you found a supplier on the East Coast, probably Georgia, it would be less expensive than shipping; and your trees would be less stressed in transit.
I don't have (yet) direct experiencing companion planting in a pecan orchard. However, from life experience I can tell you pecans (all hickory family) can be found interspersed with a variety of trees. They are not picky about their neighbors, unlike black walnuts. One finds
native pecan stock volunteering in hedgerows quite willingly.