Dynamic IP shouldn't be a problem if you're the one initiating the VPN connection (outbound). However, inbound VPN can be a problem and can usually be addressed by using a dynamic DNS service.
I am on dynamic IP but I am still able to VPN into my home from anywhere using dynamic DNS.
BTT:
Instead of disabling the WiFi on the CPE router, you can add a 2nd wireless router and set its WiFi to the same SSID and PSK as the first one. That will extend the coverage of your WiFi. Just follow best practices when allocating the channels (use non-overlapping channels) and make sure you're not using a channel that is already occupied by you or a neighbor.
In this setup, you won't use the routing and DHCP functionality of the 2nd router. You're only going to use it as a 2nd switch 2nd AP.... a wired extension of your network, if you will.
