1)When your subscription expires backup will no longer be functional. You should download and save the One Care restore tool should you need to restore One Care backups in the future -
http://social.microsoft.com/Forums/en-US/onecarebackupandrestore/thread/e5d686c8-762b-4b22-bc08-bfb93f911e572)You cannot install another antivirus program without first uninstalling One Care.
3) See #2.
Jim
Microsoft MVP Consumer Security - Forum Moderator - Live One Care - Live Mesh - Microsoft Security Essentials