My first rows of trees are about 15-20 feet. I then started to plant them 20-25. Some people preach spacing, but almost every orchard I have been to, the branches are pretty much touching each other in the rows, with enough spacing in between the rows to drive there machines through to spray, and pick the apples.
About 2004 I started planting apple trees, usually about 4 per year. Then I took a break for a few years, then I opened up a larger area, and planted more. I stopped trying to over think things and just plant trees where I have an opening. I have even started to plant them inbetween rows, because I had space, and I feel the deer would feel more comfortable with a more natural orchard.
My trees are still rather young, anywhere from 1-17 years, so maybe as they grow bigger, I may regret it, but so far I don’t think it has bothered the trees at all.