You can’t create custom faces on any Apple Watch. There are apps that pretend to do so, but they are just apps, not watch faces, and don’t work as such.

If your partner always carries the phone, the cellular connection is unnecessary and adds no functionality except the ability to make an emergency call (which can also be done on the phone, of course).

I have no idea what you are trying to ask.

Have you tried an even harder boot by unplugging and replugging it?

AppleCare+ covers water damage. The standard warranty does not. Perhaps base your decision on what coverage you have.