Good luck. When my son was planning unofficial visits to schools for XC/Track we found that coaches tended to be slow to respond with confirmation, but nearly every one sent an email a day or two before we left for the school–after we made the decision to visit the school whether we saw the coach or not. I think that might have been a way to sort out student athletes who were really interested in the school. I think you have the right attitude on the unofficial visits.
Coaches will have drastically different attitudes and strategies on official visits. Some teams invite 5 or 6 recruits for every spot, and some are much closer to 1 to 1. I know at least one school that has stuck to OVs in the fall of senior year, and at least one that has started hosting OVs in junior year. It’s probably easiest to ask about an OV in the context of an overall discussion with the coach on their recruiting process and timeline.