Excellent advice from Midlo. Short but sweet. Often enough to demonstrate sincere interest with meaningful content, but not overwhelming.
Regarding the pitching coach, our rule of thumb was to include someone other than the recruiting coordinator at a D1 only if there was a personal relationship established. For example, if that Coach talked to you, knows your name, asked you to follow up, etc.
But you should definitely reference that you've been at a given school's camp in your initial email to that school.
For example: "I am very interested in playing ball for Acme College. I attended your prospect camp last month. My family and I also did an Acme campus tour and orientation session." This shows a sincere and deeper level of interest than someone who's just sending out feelers to a coach.