The SIG SAUER Romeo 3 Mini Reflex Sight w/Riser, 1x25mm, 3 MOA Red Dot will not fit the P320 AXG Combat.
No, the SIG SAUER Romeo 3 Mini Reflex Sight uses the C-MORE standard footprint. Your GGP slide is dual cut for optics with either the Leupold DeltaPoint Pro or Trijicon RMR footprints only.
The SIG SAUER Romeo 3 Mini Reflex Sight uses the C-MORE standard optic footprint. So you would need to use the #4 plate with screw type A included with the optics ready M&P 2.0 10mm. If you do not have an optics ready model, you would need the EGW adapter plate found by using the link below:
https://www.opticsplanet.com/evolution-gun-works-vortex-razor-mount.html
The Sig Sauer Romeo 3 Mini Reflex Sight uses the C-More Standard optic footprint while the Sig X-Carry Legion uses a DeltaPoint Pro footprint. So you cannot fit this optic without an adapter. You can fit the Romeo 1 Pro, DeltaPoint Pro, or any other optic with the DeltaPoint Pro/Shield RMS footprint.
I cannot find anyone that makes an adapter plate for the PDP.
Yes, it would fit and function perfectly.
Yes, you would just need to use the adapter plate for the C-More standard.
Yes, it will fit and function perfectly.
Yes, you would just need to replace the rear sight with an adapter plate such as: KK-RMT-VRMSM-49432
Yes, it should work just fine.