There is a very nice hardware/software guide here https://www.hackster.io/naresh-krish/getting-started-with-the-rak-831-lora-gateway-and-rpi3-e3351d?
PI pins >> https://developer.microsoft.com/en-us/windows/iot/docs/pinmappingsrpi
Just followed this for the basic PI setup, I stopped before the wifi part as I am using wired ethernet, then I switched over to the new TTN packet forwarder setup guide, I think you need to have basic linux skills to get around things mind (mine are very basic but improved in the last 24hrs) - I did try the older packet forwarder first and then installed the new one - no issues. I only mention the old one as it did seem to install drivers from memory.
Only done basic testing, its indoors and getting lots of 'WARN Uplink packet received with an invalid CRC error - ignoring" but testing my own device both uploading and downloads are working it seems.
My first multi channel gateway so a) wasn't expecting any other packets to be coming is given the lack of gateways in the area and how remote we are b) not sure if CRC errors on incoming packets is just normal and simply down to being indoors on test bench with noise interference.
Interestingly, I have single channel Dragino LG01 working and I'm sure there is no CRC validation on those, even this picked up 2-3 packets each day from unknown devices.
It would be useful to have pin reset script in the build I think.