Midwest Mom,
My best advice is to treat this like a 2nd or 3rd date. Clearly they are interested and clearly your son is interested. It is time to really focus in on the relationship, and expectations. So, I think the best way to understand all of this to put a timeline on it. So, my son would ask the coach about the remaining recruiting timeline, expectations and requirements. You mentioned D1 high academic so I would make sure your son has all the boxes checked or ask what remains to be done to receive an offer...in other words where is he on their recruiting list. Then he'd move into the possible daily routine when he arrives at school for Fall practices, winter session, Spring season and possibly summer college baseball. It is incredible how scheduled your son is going to become so why not ask the question from that perspective. My son was an engineering major so we knew there were going to be time challenges. You may want to ask the question from your son's prospective major.
I think what you'll find is the daily routines are different from one program to another and they vary by position players and pitchers. He absolutely needs to understand this typical daily routine. In addition, during the un-OV he would request to spend some time with his future position coach and the strength and conditioning coach. They are going to have philosophies about how to do things, when to do them and frequency. Your son is going to be spending a lot of time with these people. Again, he needs to know how they do things in advance and feel comfortable with it.
Dress appropriately. Yes khakis and polo or something similar. My son grew up in the South, so he is very familiar and comfortable with "yes, sir" , "no, sir". The D1 high academic teams that he did un-OVs with in the north got a kick out of that and they told him when he joined their team later. Again, do & say what is comfortable and respectful. It is a start in his profession career of baseball or something else. Treat it that way.
As always, JMO. Good luck!