Mowing the land

This is where the Pawpaw patch will go.  I will bring water to here but want to wait to plant until the mulched up wood breaks down another season.

Planning and Advice request

I want to plant a 1.2 acre orchard of Pawpaws.  This is land we purchased last year, had some weeds, brush, and small trees growing on it.  We had a large brush cutter cut all this back, last fall we put out clover.  We plan to let the land sit for a year, let stuff break down.  Nearby land is a little acidic.

We currently have three pawpaws.  Brief youtube video should follow.  We planted them in 2009, did minimal fertlization each year, they have only had water for two years.  We have a deep well with 70 GPM at 40 PSI possible.  While we love the Overleese flavor, not sure it makes sense to try and grow more of it given its relative stunted growth.  Video follows:  https://www.youtube.com/watch?v=CQW2Niw9HR4

Currently we have 48 stratified seeds from our pawpaws planted.  We picked up 200 more seeds from Peterson varieties.  The plan is to let these grow in pots for a season or two, graft if/when scion wood available, transplant to the land.  We are located in Eastern NC.  Land shape is as shown on following photo.

If we did straight rows we could potentially do 20-30 varieties.  One green World currently has 14 or so available.  I think we should buy one of each variety that we would grow to use for scions.

My questions are this:
What spacing? 
Best irrigation method?  We use Hunter PGP Ultra pop ups right now, familiar with them.
Grow many varieties or narrow it down?
Would Overleese maybe perform better on other root stock?
Long term fence strategy?
What else should I be considering at this point?

Thank you!