The groups facility will be very powerful in the following ways...
You will be able to start a group - Suppose you call it X
X can have members - though they do have to be z free members or sustainers - but the former is zero cost for them
They also do get personal zspace pages of their own, even if they are only free members, though they can ignore it
X itself gets a page
The X page gets admins, you - the initial creator - first, and then anyone you choose.
The admins of X can add people to X - and there is a link on X page to ask to be added. So if I want to join X I click the link on the X Page, all the X Admins get an email asking to join, and they can accept me as a member of X, or not.
The admins of X can change X page- including the entries in its top tab menu and the sub menus under the tabs, its left menu, and its content boxes. It is entirely customizable by X admins.
And the filtering of content - in menus or for what appears in content boxes - can get select for any kind of content from the whole Z site - but also for any subset that is by X members, about X, etc.
Everyone visiting can see X page
X also has a blog for all its (sustainers members who have blog access) to post in, and everyone to see. Commenting on X content is possible. If X members upload photos of themselves, or photo albums, those can be in content boxes on X Page. And so on...for chatting, commenting, etc.
So I would say f you have to do a page for your project sooner - perhaps, don't overdue it, because once the groups exist it will be very easy to move content to the group page...and most likely, it will be much easier to put in graphics, blogs, menus, and so on, in the group page X Page...
In essence X Page is a site that has the same navigation and member facilities at zcom though revamped and redesigned to fit X needs - in which any X content can display, but also anything from Z you might want there, and in which admin of X is by X admins, not by me or Chris...
Finally, of course we are doing this PRECISELY so people like you can use it however you decide. A publisher might create a Group for them and all their authors, ditto for any project, movements, or even organization. You get a free, hosted, web site, with incredibly rich features, entirely under your own very easy administration...