BuddyPress.org

obviously yes.Just turnoff the blogging and let the users register for the username only.So you have all the features except the blogging there.

and as far as server requirement is concerned,when blogging is turned off,the database size is small enough for your server and load is just ok ok.

Again,this is what I think with my experiences, and I think,wpmu+buddypress is best suited for your need(better than elgg ,as the wp community is much more versatile than the limited options available with elgg).