The wiring connects the PC to the hot shoe so yes, it's just an open circuit. insulate the ends if you're going to tuck them inside.
The shoe is indeed removed from the inside so the cover has to come off.
As above re: the holes, one large, four small uns.
Filling the holes without some backing material may be tricky, the metal of the cover is too thin to give much support. Take the cover off & you can use a bit of fiberglass cloth or thin brass/aluminum
If you want a bit of FG cloth PM me. I've used it with regular slow cure epoxy & it works fine.