Your fiber ONT box (where the fiber signal gets converted to copper ethernet) probably has a backup battery in it. This is especially useful if you have VOIP landline phone service through your fiber provider so you can call for help if necessary when the power is out. You or your provider will need to replace this battery every few years, just like with a UPS.
Agreed. Theoretically possible, but practically not possible unless you are an embedded hardware engineer with access to Sony’s datasheets and potentially crypto keys. Some sort of external box is much more practical.
assfish are soft and flabby
Your domain name could be ordered to be removed from US-based dns providers, no matter which TLD it is. That would essentially block your website from most US-based viewers without actually shutting down your hosting. Advanced users could still get to it, though. Consider hosting through Tor and a .onion address for more resiliency.
Assuming that you trust what Proton says, when they receive a (possibly unencrypted) message they re-encrypt it with your key as soon as possible and they don’t log the content. So, after that point, they (or anyone else) can’t read the email contents. If it was also encrypted in transit, then there’s only a small window inside their email processing system where the plaintext was passed from one encryption to the other. It’s only decrypted again in your browser or proton mail app with the key that only you have. It’s not bulletproof, but it’s better than most providers.