It already does “act” like a member profile in the ways you mention…lots of folks use Groups as you say like “the pages in Facebook.” There are plugins that can extend the groups functionality more. but all in all…i think if you just change the language of the group component you can have something very much like that of FB.
“post on wall/wire/comment/updates” – the activity stream on the group is the wall.
“create posts” – I don’t know exactly what that means…but there is a plugin I’ve seen that allows groups to manage it’s own blog where group members can make posts. thats in the plugins under the Extend tab.
What specifically are you trying to do?
