A garmin MFD can not control a raymarine autopilot, nor can it see raymarine radar output.
For Radar, MFD and autopilot, you want to carry the same brand. For vhf, ais, stereo, GPS receiver, etc you can swap brands without giving up much functionality.
I was told by Raymarine that a Gamin chartplotter CAN control a Raymarine autopilot, but you can only have one MFD controlling the autopilot at a time. I have not tried it myself yet, but am planning to.
I agree that the Garmin MFD cannot display radar from the Raymarine radar antenna.
I have Raymarine radar, E120 MFD, sonar/fishfinder, and autopilot. I have a Garmin 742xs MFD, and a Standard Horizon VHF iwth AIS receiving. I can show depth on both the Raymarine MFD and the Garmin MFD, but fishfinder only through the Raymarine. I can receive AIS data through the Standard Horizon VHF and use it to show vessel position info on the Garmin. Right now I'm controlling the autopilot through the Ray E120, but (as mentioned above) I've been told I can switch which device is controlling the auto pilot, and plan to try that out once the boat launches. I control my Fusion stereo through my Garmin. I bring in SIRIUS weather and show it on the E120, and I've read, but haven't tried, using that same antenna to send the SIRIUS radio signal to my Fusion, because a stand-alone antenna was cheap and easy. I use a combination of NMEA0183 and 2000, in addition to the Raymarine networking.