I was a prior MIDN in Navy SSMP (An ROTC-like program that commissions Reserve Officers out of the Maritime Academies). I took Applied Calculus, Chemistry 1 w/Lab, English Composition, and two major classes pertaining to the Merchant Marine. I also had Military Lab on Mondays, PT on Wednesdays, and Rifle Drill on Fridays. Your DS's schedule looks fine. It closely resembles Plebe Year. Doing well (A's and B's) shows USNA you can hack it in a college setting. ROTC is always a good addition as it shows a desire to serve, regardless of branch. I took only 15 units my 1st semester and I found that to be manageable. With respect to taking a full year of physics, you could go either way. USNA only looks at fall grades when reviewing college applicants, but USNA requires its students to take Physics 1 and Physics 2. Each are a semester course. It also wouldn't hurt to get a background in Chemistry. Calc and Chem are known as "Plebe Killers." Have your DS check if he can fit intramurals or a club sport into his schedule.
Lastly, I will say that since your son is ROTC, he is eligible to receive a nomination through ROTC in addition to his respective Members of Congress.