My daughter’s experience with a transfer student was in her junior year. She attended Davis and a couple of the girls were moving out of their rental townhouse so they needed two roommates.
It turns out that one of the roommates kept in contact with a HS friend (from SoCal) that did the community college route and was transferring to Davis. The girls contacted the transfer and asked her if she had found housing yet. She indicated that she was looking for a rental through the housing office; they invited her to come up for a weekend and check out the townhouse. She accepted the shared room and became one of the roommates.
Just a suggestion but maybe if your son keeps in contact with some of his high school classmates, who are at schools where he is planning to attend, he could use that resource.
Another thing, the students at Davis refer newbies to wikidavis. It’s very helpful.
https://localwiki.org/davis/Welcome_to_the_Wiki
I don’t know if the other colleges have something similar.