Sounds like your son has a lot to offer a good collegiate program. My advise is to go at it from a reverse engineering method. First, make a list of the schools which have his intended major. They should all have solid info on board test passing and job placement rates.
From that list, determine his potential chances for being able to compete. Some P5 level schools may allow walk ons, but the # of meets you get to go to may be greatly limited. It's not much fun to bust your tail and not get to go to meets. I walked on at D1 and I've coached at all 3 Divisions of the NCAA and I can speak to the great experiences to be had when kids find the right fit. A big issue on many D1 programs is roster limits brought on by Title IX/Gender Equity considerations. Make sure you know that up front. That is usually not as much an issue at D2 and D3. And you don't see many D2 or D3 men's programs being cut.
Hope this helps. I wish you and your son the best of luck determining the best fit. I would not trade my experience for anything, but the landscape is vastly different from when I competed in the 80's. I would not be permitted to walk on to the same team under current constrictions.