There are no rooted FTF files available. FTFs are unmodified stock firmware packages. You will find that the prerooted roms available are in zip form and require flashing via a custom recovery.
As for restoring backups made by the Sony tool, you should be able to, as long as your backup is from the same firmware version. You cannot restore backups made on 4.2.2 on a 4.3 rom, for instance.
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