how should I set up a page for friends to register on our site and enter their profiles. Example, students from the year before and year after, Teachers, etc?

I'd suggest setting them up as you would any classmate but check the box to have them listed as guest members. That way they can have access as a classmate but not enter into your statistics regarding classmate participation.

Check out my site. I set up faculty/teachers as Guest Members.

I have a few teachers and a few people from the year before us and the year after us, as well as a guy who went through the first eight or nine years with us, before moving, listed as guest members with access to the classmate profiles. It's rather easy to do. Good luck with your site. Tam