If I was in the wedding party, I’d wear my Tag Heuer. Anything else and I’ll switch to the leather link band most of the time.

how many iOS versions can I update on my phone till I can not connect the 2 devices?

Theoretically, forever. Each watchOS version requires a minimum iOS version (e.g., watchOS 10 requires iOS 17 as a minimum), but it doesn’t work that way in the reverse - iOS 17 should be able to pair with any watch going back to the original Apple Watch, as will iOS 18.

That said - people do occasionally have issues when pairing doesn’t happen. But it is supposed to work that way. Currently I use an Ultra but I have my backup Series 5 still on watchOS 9 but it remains paired with my 13 Pro running iOS 17.1.1 (I had to unpair both watches when I did a factory reset and restore of my phone last month and re-paired both watches just fine).

Anytime I have used a screen protector that had a lubricant spray (basically it is just water with a very small amount of soap/detergent) that was used to help place it correctly without bubbles I ALWAY sprayed on the screen protector (and my hand, to prevent sticking to my hand), NEVER NEVER NEVER on the device.

This person who did this should not do it that way.

You probably can’t complete your challenge anymore. If you have, say, a challenge that says “Get 75 exercise minutes for 14 days this month”, and you have done do only 6 times so far this month, and it is the 24th, then you don’t have enough days left to complete the challenge and the challenge disappears from your watch and fitness app.