Some random resources to help setup Zerotier :
https://github.com/zerotier/awesome-zerotier
https://github.com/joylarkin/awesome-zerotier
Your own self-hoted Zerotier Controller :
Configuring Zerotier on OPNsense
https://docs.opnsense.org/manual/how-tos/zerotier.html
Locking down the zerotier network so only certain networks are available :
https://blog.reconinfosec.com/build-a-private-mesh-network-for-free