Backup questions - incremental, system, etc.

Questions on backup. I have weekly incremental backup configured to 1 retention. When it failed, it created 2 directories as intended. 1 working backup, 1 failed. Q1: If I run force backup, will it compare from the failed backup and only save changed files, OR will it save a whole copy of a new backup consuming disk space? Turns out it did not replace the failed backup, it's still there. Can I make an rsync copy/replace for the two dirs replacing the failed weekly backup, with a forced backup? Q2: Can a system backup, be used to restore same cPanel server to a new server? Q3: Can a /var/lib/mysql system backup be used to restore a whole MySQL server in case it fails? Does a simple copy/paste would work? Q4: How does one restore a system backup?