Does this clipped-sine oscillator need a buffer?
My opinion is it does need biasing but you can use the MCU's crystal mode.

I recommend the XO mode where I believe an internal &lt;=1M is used for DC feedback from Xtal 2 OUT to 1 IN

I think the 5M shunt has some minor benefit on startup, but I can't verify that.  100pF is  adequate (100 Ohms) to couple the clipped 0.7V sine wave to XTAL1 input.  The unbuffered inverter inside the PIC on Xtal 2 Out should have voltage gain >10 to saturate output.