Hey,
I've recently completed a project that had similar ambitions to this that had to be toned down slightly.
The simple answer is yes... well... kinda, maybe... errr.. but not easily. CMSMS isn't really designed for this kind of site, but it can be bent into shape slightly.
Front End Users (FEU) and Custom Content (CC) is an immensly powerfull combination that your definately going to need to use
- - FEU allows users to register on the site
- - CC allows you to control how a page is generated dependant on if a user is logged in or not.
I've heard Form Builder and Form Browser are a powerful combination
- - Form Builder, perhaps you could use this to make the forms that users use to update pages (really not sure)
- - Form Browser, perhaps you could use this to make the pages you want display the content submitted by forms (really not sure)
I'm reasonably sure you could handle the comments feature using the comments module (NO WAI YES WAI

) but you may need to get your hands dirty with php and smarty to intergrate precisely how you want.
Hope this helps
Richard