I would check on the Frontier forums, might have more people familiar with the TV side of things over there.

As for the Internet, you don’t need the gateway, just credentials for PPPoE

Where do the STBs coax lines connect to the coax feed from the road? Surely the Frontier Gateway isn’t acting as a coax splitter…

Yes you can bypass the gateway altogether.

I do this directly from the ONT into UDM-Pro/SE with a few customers and it works great.

Can’t recall for certain off the top of my head, you may need to get IP details or other info from Frontier to plug in to your own router… PPPoE perhaps…

I’ll dig into a customer’s config and get back to you.