best use of users, workspaces, groups

best use of users, workspaces, groups

Hi,
I have 5 people who need to collaborate on 7 documents.
Not all people work on all documents, usually only 1 - 3 people per document.
I have set up workspaces for the 7 documents (one each) and have asked the 5 people
to each register for a free account so that I can invite them as User to the various
workspaces.
Is this the best way of doing things? Or should I have just created a group, invite them
to participate and only then invite them to the workplace?
Am a little lost/confused about how workspaces and groups best work for me.

Any input welcome!

Thanks.