Regarding Fall Baseball with a Travel Team vs. High School team: I wholeheartedly agree that it should be one or the other to prevent overuse or fatigue. That being said, make sure the juice is worth the squeeze, IE: is your TB team playing a similar amount of games and similar completion as your HS Fall team? If so, is the cost worth it?
Bottom line, just make sure which ever direction you go, your son is being developed properly without overuse or without breaking the bank before he's even step foot on a HS field.