Here is what I am looking to do for my site (please help me figure out what modules I need):

1. I need to be able to not allow new user registrations - I create the logins and that's IT!
2.Has to be as secure as absolutely possible (site will contain very sensitive information for registered users only)
3. Need registered users to be able to start topics, reply to - like a forum - but also attach/upload files to that post or replied posts.
4. need a form for customers to enter comments - but only registered users can see/view the customer comments
5. Registered users are the ONLY ones that can see ANY content on the site (other than the customer comment form obviously)

Thank you so much for all your help!

hmmlgm, Welcome to the XOOPS forum!

1. There is a setting in the general profile preferences: 'Allow new user registration?
' Yes/No.
2. The permission settings can very flexible declare which user groups have access permission. Many modules have additional permissions on (sub)category level.
Additional measures could be taken as eg Apache paswords, https, etc.
3. This forum NewBB/CBB 3.08 has the possibility of uploads with a post (available for some user groups).
4. This is the most dificult. There exist modules to fill in forms, but the results are mostly sent by email. Reproducing the forms other then to admins is in general not there.
Maybe Formulize can do it, or some customers helpdesk modules as eg xHelp.
5. See 2.

You can check out some modules and functions at your local PC with eg XAMPP.