MC,
You have received a lot of great feedback. And you have some elements of a sound Summer plan already.
Many families with a profile similar to your son's focus too much on playing games the Summer before the player's Junior year. Local leagues, travel tournaments, big showcases, getting seen by colleges, etc. That can be great if the rising Junior is ready for that exposure. But many are not... yet.
I recommend to players at this stage to focus (as others have noted) on: standardized test prep; getting bigger, faster, stronger; and on further developing baseball skills.
As a family, I recommend visiting some colleges to begin getting a sense of what fits: urban, suburban, rural; small, medium, large; in state vs. out of state; 2 year vs, 4 year. And then beginning to compile that first (and it will change over time) target college list based on the intersection of where you son might be able to play AND be admitted.
Baseball tools matter. My 2016 spent time at the TX Baseball Ranch a couple Summers back to work on improving throwing velocity...and he ultimately gained a solid amount of mph. He began serious strength, speed, and agility training and was able to put on weight and get substantially faster. He worked regularly on his batting with a private instructor. These are all things that can be difficult to do during the high school season because of time constraints.
He played in about 8-10 baseball games, but all locally.
Academics, particularly test scores, matter. He worked on ACT prep and eventually scored 6 points higher.
We made him work so that he had his own spending money. He volunteered for a week with his youth group. We went to church as a family. He had free time with his friends. I say these things only because we lived a little bit with our 2012 and realized that a better balance was needed, i.e., not all baseball all the time.
Good luck!