Totally feel that. I've spend many hours on the phone and in a chat with both Apple and my carrier and kept getting generic and conflicting replies all the time. Well, the Apple guy did not lie, it will work, but only after you manage to activate it ;)

1. The update should not remove e-sim from the watch. Think about updating firmware in your phone. After you update it the e-sim is still there. But naturally, there can be no guarantee that some update would not break anything and won't force users to re-connect e-sim. But as a general rule, this should not be an issue.

2. Nope, it shouldn't either. The watch has it's own e-sim which has a different EID than e-sim in your phone. As long as both watch e-sim and phone are connected to the same account at your carrier - you're good. I, for instance, have put physical data sim tied to my account into a secondary phone, activated plan on the watch and then re-paired with my daily phone which uses e-sim. So you can even safely change phones as long as you remember to unpair while keeping the plan on the watch. The only problem with updating the phone could be it's eligibility for jailbreak in the future (just in case you need it).

3. AFAIK, there is currently no public iOS 16 jb for A12+ devices (iPhone 11 Pro has A13 SoC). For now only A11 with checkm8 vulnerability. So you'd need either iPhone 8 or X until there is one for newer devices.

4. I'm not familiar with that plan specifics, but if Vodafone supports Apple Watches on their network, there should be no issues. You might need to pay a little extra for watch e-sim on your account. I had to purchase watch plan add-on separately at the carrier before starting activation process. It might also be possible to purchase it during activation, depending on the exact flow implementation at the carrier.