Its quite complicated to setup as well, just went through the instructions and its a long way from just add to docker and run unfortunately. Would be nice to be able to just get a runner in the same or different docker and it just works easily without a lot of manual setup in Linux of directories and users and pipes etc.
I did the same move from contabo to Netcup. Contabo I had all sorts of weird bandwidth limiting problems that I couldn’t explain and which the continued to deny they were throttling. Netcup worked perfectly.
So many of the GPUs have been crippled for the purposes of gaming and there is zero incentive for Nvidia to produce drivers for those cards to do anything else. Alas they will just end up in landfill.
The DMZ for the ISPs router forward to the second router, then everything that hits your outside IP will be forwarded to router 2. Then on Router 2 you open the ports for your service and forward to the internal machine. That should all work fine.