Business Accounts: Those of you who have a static IP with coax and your own router - VPN architecture question

So we have Comcast business and currently rent their box. I'd like to bring in a managed router and get a static IP, however with a Coax plan, you HAVE to use their box and assign the static IP to the comcast box.

My question from a VPN perspective is if my BYO router is a VPN server and I want to connect to it from home using my public static IP, I will have to put the comcast box into bridge mode and set up port forwarding to send VPN connections to my router so the router can authenticate, is that correct? I am just wondering how I can VPN to my network and authenticate on the router if it is the comcast box that has the static IP, not the router.

Just looking to get some feedback here.