Well employes are “users” so they will work with target lists and campaigns. However, if you create custom modules for th rest, they will not work with campaigns. I’ve tried a number of times to get this to work by customizing the code and get so close but can’t get it to work. So my advice would be if you are planning to use email campaigns to send to these various types of contacts. Then they should all be LEADS or CONTACTS. Just add a field for “contact type” and that makes it easy to idenfify, report and segrate your contact lists.
I built a CRM for an online school with all the same issues. Everyone is a contact/lead except employees and teachers, they are users.
Students are are further segregated by “active”, “graduated”, etc.
You don’t need accounts at all. (there are alot of cusotmizations to apply to disable accounts throughout, including removing subpanels, removing from the conversion dialogue, etc.
Opportunties are not relevant either. Basicially you have leads (of any type) that convert to Students. Students eventually become alumni by changing their status. Parents and volunteers probably won’t be a lead , just contacts type= parent or type = volunteer.