Configuring OS X Lion as server (without server.app)
I would do it this way


Configure Time Machine in you Mac Mini Server 
Share HD2 or create a shared folder in HD2 to save the backups from your MacBook
Configure Time Machine in your Macbook to save on a Network folder (The shared folder in your MacMini)
In your Mac Mini enable screen sharing and remote login (this last one for SSH)


Make sure your firewall in your Mac Mini is set up correctly to allow incoming connections