_XINST_OFF_4L disables extended instruction set, which you'll always want disabled on any 18F part that has it when using PBP.

The unprogrammed default for this bit is ON unless you disable it as shown above.

Hint: Look in your default PBP header file for what they show there.

Yes. If the PIC is operating at 32MHz, then you'll want to define it just like you would for any osc speed.

Write the value 'shown in your datasheet' to OSCCON to set it for 8MHz. Then flip the bit in OSCTUNE to enable PLL. It should then be running at 32MHz.