I think you are ahead of the game and in a great place to help your son successfully navigate a difficult path.
My only addition to the grades discussion is that I agree- it’s important to keep the grades and rigor up-- our S chose all test optional schools to apply to (5 total, 3 colleges/unis with music schools or conservatories) and never took the SAT or ACT. He felt his time was better spent prepping his audition pieces, however, he maintained a 3.98 gpa throughout HS, which I think helped with the academic acceptances.
Summer programs were all online at the time due to covid, so he could do multiple programs and got a lot of exposure to a variety of college faculty, but also it helped him to see where he stood compared to his peers.