Casbalti You can install batocera on the internal disc. Start from USB Stick and boot Batocera from that stick.
Then go to the menu, "system settings" and then "install batocera on a new disk".
That is the way i use it, too.
If you want to play PAL and NTSC games with sound, you have to choose an 60Hz video mode.
For me the 1280x720 Video mode did 60Hz.
You can choose it for specific emulators when you go to menu, "games settings", "advanced", then the emulator you want to change the video mode and then "video mode"
NTSC only systems like PC Engine or Arcade like FBA need 60Hz to get audio. With a 50Hz Video mode you get silence.
Keep in mind, that PAL games with a 60Hz video mode judder when the game scrolls fast. NTSC games with 50Hz video mode judder too.
With some games that is noticable, with some you wont notice it.
But if you only want to play PAL games on your 50Hz TV, you have nothing to do.