Help with flashing rom
Backup stuff with apps like Helium or Titanium Backup.

Custom recovery is required, while root is not; however you often need root to flash a custom recovery.

Recovery stays in its own partition and will not disappear, unless you deliberately chose not to remove a script that replaces it with the stock one (this mostly happens on stock ROMs).

It's usually safe to restore data for user apps; however do be careful when taking care of system apps - especially don't just backup and restore data for Settings.