RPI Server UPS and Backup Network


I run a RPI4 based server at home with OMV and a couple docker containers and would like to make this survive a power cut while also keeping internet connectivity.

I came across the Power Management Hat have a couple questions:
Can I run the software for the online access in a docker?
I try to avoid installing anything along OMV which doesn´t keep config files after reboot unless its in a docker.

What do I need if I want to have a backup internet connection via 3g or 4g?

I want to put together a system where upon power failure it automatically switches to the mobile connection so the server remains accessible from the internet.

Do you offer a case that fits all the required components nicely?