RE: NEED INPUT FROM INSTRUCTORS, TEAM RIDERS, STARBOARD TEAM, TESTERS...
Here's my take on this.
I don't have any '07 Starts as I do not like the wheel on the back, so I have a Rio M.
It works fine for beginners up to about 175 lbs. For heavier sailors I would recommend the Rio L.
The Phantom is great, and would be my suggestion as the "follow on" board to the Rio.
The Apllo requires such large, heavy rigs that I would not think it a good choice for a school rental operation.
If the winds are 8-10 knots min. maybe have just one and a 10.0 m2 rig for people to try, but it's not an entry level board by any stretch of the imagination.
The Serenity would be in the same category as the Apollo, to advanced, but again having a couple of them for progressing sailors would keep interest going when there not enough wind for anything else.
I don't have (also have not sailed) any of the Hybrids, so I cannot really comment on them, but they seem too advanced for sailors at the entry to intermediate level. They are race boards, and unless you plan to hold races, they really aren't applicable to a school.
Hope this helps,