Do I need business plan?

Hi,

I have a school about 500 students. I intend to use Zoho for the students and teachers to interact

Currently the activities I have in mind are:
-email
-chat
-calendar
-document sharing
-wiki
-forums

Is there any problem with 50 students/accounts accessing Zoho at the same time with 1 same IP? I mean, can each account still use free account.
If not, will Zoho require me business account? My school is private school, what plan should I looking at, any discount?

Thank you for the great stuffs.