Several types of file are excluded from a backup as they are temporary pagefile is just an area of disc space put aside to use as temporary memory when all the RAM is in use.
I never do differential backups I always do a backup weekly using two different file names so if one get corrupted I have another to fall back on.
Recovery media is basically the program on a boot disc so that you can restore an image if the machine fails to boot. A MUST DO
Only needs to be done once however if you upgrade the program make a new recovery disc with the latest version as old recovery media may not access newer program backup files. The recovery disc does not contain your backup images these need to be on a separate hard drive preferably external as a PSU failure may take out all internal disks.
Only ever used the program in anger once and needed to do it from the recovery media as the machine would not boot and windows was non accessible even to an experienced system restorer.