1) above tiller works for me (including position feedback).
I guess the question about the motorcontroller and arduino are because you want to make them yourself. (I just bought them pre-build).
2) Either TinyPilot or OpenPlotter can be used to export the IMU data to OpenCPN (I use the tinypilot with signalk).
OpenPlotter can be installed on top of Buster.
3) I thought B&G / Navico / Simrad / Lowrance require 10Hz HDG on a specific NMEA network, but check the details form the supplier.
Should be possible with SignalK (untested, since I have no radar).
The only question I have about your hardware is whether the RPI3+ is fast enough for radar.
But if you already have an RPI3 installed I would worry about that later.
I guess the question about the motorcontroller and arduino are because you want to make them yourself. (I just bought them pre-build).
2) Either TinyPilot or OpenPlotter can be used to export the IMU data to OpenCPN (I use the tinypilot with signalk).
OpenPlotter can be installed on top of Buster.
3) I thought B&G / Navico / Simrad / Lowrance require 10Hz HDG on a specific NMEA network, but check the details form the supplier.
Should be possible with SignalK (untested, since I have no radar).
The only question I have about your hardware is whether the RPI3+ is fast enough for radar.
But if you already have an RPI3 installed I would worry about that later.