MFD is configured by using the Installation Wizard to output the following NMEA 0183 sentences on NMEA0183 Port 2. (Installation Guide doc from Furuno is quite good).
a. BWC/BWR (Bearing/Distance to Active Waypoint)
b. GGA (Position Fix)
c. HDG (Compass Heading, Deviation and Magnetic Variation)
d. HDT (Present True Heading)
e. RMB (Waypoint Information)
f. RMC (Time, Date, Position, Course, Speed and MagVar),
g. VTG (Track and Ground Speed)
h. ZDA (UTC Time, Date and Local Timezone)
The Data Port 2 connections from the MFD are available inside the Junction Box behind the instrument console. If your set up is the same as mine, you will find the red and red/white connection wires from the Port 2 output unused, but already connected to a 'chocolate block' (terminal block). Its a trivial matter to connect up in that JB. Wiring diagram in the Furuno MFD installation manual describes the cable details.
Interesting question about your WiFi gateway. The simplest way to make the data available externally is from that Port 2 MFD connection, it will output just about everything you could need. However, if you are trying to access data when the MFD is NOT operational then you'll need to source from the Hydra CPU. Assuming your GP-150 is connected to the Hydra CPU (as per my original Amel setup) then the Hydra should echo position and time, as well as providing its native wind data, depth and STW. You will have no heading based information because the PG500 compass is connected to the MFD directly.
I understand the Hydra CPU only has one NMEA output, and this is connected to the MFD Port 2 Inputs. You can piggy-back a connection, but for permanent use I would try to find a proper 0183 sharing device (one input - two outputs, I haven't looked but I'm sure they must be available). One problem you might find is that a dead/un-powered MFD may affect the shared output and wont give the fault-tolerance i think you are looking for. In this case you'd need to disconnect the faulty MFD port 2 input connection. (Can be done inside that Junction Box I mentioned).
Hope that helps, feel free to email me directly if you want to talk in deeper detail.
I've now mapped out the wiring/interconnections of my system on paper, and when I have some time I'll prepare a full system schematic and share it.