In our experience, two tours a day was a lot. It doesn’t seem like it would be, but it was, for us. I think if you overdo it you run the risk of your child just not going on the later ones, or checking out, or getting burnout on the process when you are really just getting started. One school a day is better. And at the 3rd or 4th school, the tours might all sound the same and blend together.
We may have done Elon and WF on the same day since they are an hour apart. (My son attends Elon and they are VERY GOOD at tours and presentations. WF is also great and touring it made my son realize, later, that it wasn’t a good fit for him).
Our general “flow” for visits was arrive early and do a quick drive around for a first impression and see where we were going to park. After the tour, my DS usually didn’t want to hang around much, OR go to the dining hall…I think maybe he didn’t want to be seen as the prospective student hanging around with his mom. But we always made time explore the surrounding town, for lunch or dinner.
So yes, keep it fun and not too packed. And they track electronically by name and/or email address. We’ve done our own "drive arounds’ but not an official “self guided tour” (OK actually did one of those years ago at UCLA on a school holiday, but we did have to walk in somewhere and check in)…if you are doing it on your own and don’t sign in anywhere, you can still get “demonstrated interest” by signing up for mailing lists; I wouldn’t worry about it too much, some schools don’t even consider demonstrated interest, and you can get into that later.