Are my files ok?Do you need more "proof" or smth?If you use the SafeSysUpdater build you should not be scared. It will only go through with it if you've got the correct files.
Once you've downgraded you can backup your SysNAND, then install an EmuNAND on the SD card. This will let you be on the latest firmware (10.5) in EmuNAND and have all your stuff there, install unsigned CIAs (any game or application) and A LOT of good stuff.