Setting up another Pi for Pi-Star is pretty easy, but you don't need all the "bells & whistles" of a Pi3 or 4. A Pi Zero works great for this with the proper hat. I have used both the Zumspot as well as the Chinese knockoffs successfully for DMR. I have another Pi Zero set up with different software and a DV Dongle.
I would suggest finding other groups for assistance, since it falls outside of what Jason is doing here with BAP.
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73 de N5RKE
G.A.(Jerry) Minor