Great use case!
I'm glad to know that you're digging into the community edition as well. :)
One of the community edition (CE) limitations is the number of users - limited to 5 concurrent users - and this can obviously kill the use case of a large number of users application.
However, 5 concurrent users is different of 5 registered end users.
A concurrent user is a simultaneous user session, while a registered user user is an active logon account on the applications. Active logon accounts are unlimited, but you can only have 5 logged on users, or 1 logged on and 4 anonymous which totalizes in 5 user sessions.
This will effectively limit the number of simultaneous users accessing the applications, even though you could have 100 logon accounts.
If you create your own user management architecture, you will be able to have unlimited registered end users, but will still be limited by the number of concurrent users. Not to mention that you'll lose all the permission areas and login/logout built in actions and funcionality, the Enterprise Manager integration and Role Management, and even distinguish the applications' logs by user.
So the only way, using the CE, to have 100 users accessing the application, is guarantying that only 5 at the time are accessing it ...
Hope this information is helpful.
Miguel Simões João