Making a basic social network with posting abilities

I have installed Buddypress to my WP site, and I've turned on WP multi site.

Here's what I want to do. I want a site with basic social networking ability (friending, messaging, commenting). That's why I installed Buddypress, and I think it will be fine.

The thing now is, I realize that I probably don't need multi-site network capabilities. I want users to be able to make one certain kind of post. I want them to be able to attach a PDF, write a short post about it, and select categories. They don't need pictures or videos or any other kind of attachment.

How can I have one site install of WP, with Buddypress that allows the users to do this?

If some, or none of that, makes sense, please ask and I'll try to clarify.

The site has just been set up so there's not much there (and it is still set up as multi-site), but you can take a look at