As the parent of a 2016 D1 LHP that had major shoulder surgery his freshman year in college , You don't wanna do what my son did.
He threw way too much prior to college. He was also a max effort guy, so he not only thew a lot of baseballs, he threw them as hard as he could
Shoulder surgery is potentially career ending. Fortunately , he has recovered but it was tough. Rehabilitation was 18 months. And even then, he didn't really feel right until closer to the 2 year mark.
My suggestion is you talk to the pitching coach at the school he's committed to and map out a throwing / arm care program that gets him enough work and keeps him healthy until he arrives on campus. Ask the pitching coach about any HS pitch count / inning limits and subsequently relay this information in no uncertain terms back to the HS coach. You do this. Not the player. Health issues are one of the few issues where a PARENT talks to the HS coach. And pitch counts always come from the parents. It takes the heat off of your son for having to dictate something to his coach and also keeps your son from feeling like he'll be perceived as soft
If he's a 2021 MLB draft prospect, he will want to do Area Codes, Jupiter, PG Nationals. Other than that , there is no reason to do any sort of travel ball stuff. Maybe a few innings with a college summer ball team the summer before he leaves for college in 2021