Hi,
do you want autosteer or just guidance?
For autosteer you will need a wheel angle sensor in every machine. A very common GPS receiver is the Ardusimple simpleRTK2B.
The rest of the hardware needed for autosteer is mentioned in the support files that you can find on Github https://github.com/farmerbriantee/AgOpenGPS/releases/download/4.3.10/Support_Files.zip
Maybe this also helps you: https://discourse.agopengps.com/t/documentation-of-my-way-to-autosteer/3317?u=bennet
Greetings Bennet