That's a great, specific form to use.
General rules of thumb:
1. Each individual e-mail should be short. You've got their attention, now make one point and get out. Don't write multiple page e-mails.
2. If you have multiple points to make, send multiple e-mails. Each one short, maybe 10 days to 2 weeks apart. This way, you use the topics as your excuse to contact them enough to show strong interest but not so often that you come across as a pest.
3. If you don't currently have multiple points to make, think ahead as to what points you could make. Examples would include (a) initial expression of interest, noting PG showcase and grade (provide link to PG profile page); (b) provide schedule for your high school team; (c) a few weeks later, provide a mid-season update, with your HS coach's contact information; (d) a few weeks later, inform of what travel team you'll be on, that team's coach's contact info, and the team's summer schedule.