why not just downloand the software and install it on the computer that you need the VPN? alot of modems router supports VPN.
Is there a need for connecting every devices to the VPN? I think you get 4 connections per NORDVPN account, your connection might be slowed down connecting via a VPN. NORDVPN supports openvpn, so look for a modem that supports OpenVPN, alot of the Netgears modem router does it, just check on the specs. If you do need the home phone then you can use the Optus modem for the phone and the new modem for the internet.