The lose of signal won’t matter. It happens to me all the time as I move from wifi to wifi.
For your third question, it depends on if you a have a key backup with a key security code. That’s something you should set up asap after your initial client login. If you do, then you can recover. You might want to look at github.com/vector-im/element-web/issues/16202 for more explanation. The question comes up a lot.
Regardless, I’d make sure you’re always logged in twice if you can. Do you have Element Web running alongside Matrix? If you do, keep logged in on a desktop, or laptop. Just in case you lose the phone.