My son is in a very similar position. Just started freshman year, catches and pitches. So my $0.02. I let him take the entire month of August off. No bats, no balls, no conditioning, nothing. He was over caught during the summer and it took its toll. He needed time to get healed up and his legs back. This week they have started fall HS baseball workouts and will go two days a week. Seems to be fairly laid back. He will start in a local fall baseball league coming up - 2 games per week (where there are conflicts between HS and Fall ball he'll pick one). He is also looking to get in some strength and conditioning one/two days per week, plus some basketball work. Between that, school and friends he should be busy. The basic idea is to keep him engaged but not worn out. He'll start real hitting work, catching, pitching etc. in the winter.
So I think the question comes down to how intense is the fall travel ball. If it is intense with multiple games and tournaments, I would hesitate.
As for catching and pitching, my son does both. He does pitching lessons to keep his mechanics fresh. It doesn't seem to effect his throws as a catcher. As a pitcher he has more time to think about his throw. He normally doesn't pitch all that much. Just make sure you are with a good coach and a team that can manage the workload.