Some of those EKM meters can be monitored remotely, so you could split up the farm into bays that could support say 12 miners each and 45KW of 3 phase power with one meter per bay. That way you can have a price for the space and charge for actual power used separately for a customer that can fill a full bay. Customers could be able to see power usage in real-time.
https://www.ekmmetering.com/collections/smart-meters/products/ekm-omnimeter-i-v3Also, it isn't very difficult to set up an OpenVPN server. OpenVPN access server requires a license for more than 2 simultaneous connections, but it installs pretty easy and has a web gui for setting everything up. Including creating new accounts and limiting access to listed IP addresses or subnets by account.
https://openvpn.net/vpn-server-resources/how-to-configure-the-openvpn-access-server/For miners that can't fill a full bay, you could charge a flat rate without VPN access if you wanted. If it were me, I'd not want to deal with the smaller customers though. Too much work...
