Might buy XZ Premium, few quick questions

Hello. I have a Nexus 6P at the moment but it's on it's last legs in terms of battery and performance, and I'm ready to upgrade. I just have a few questions about the XZ Premium.

1. What should I expect in terms of updates? I know they will never be as fast as Nexus, but I've heard Sony is usually fast with updates. True?

2. For the fingerprint scanner, do I have to push the power button first or does it just work anyway?

3. Camera low light performance? Is it any good?

4. Does a fast charger come in the box?

5. I'm in the United States, but I know I should buy it from elsewhere to get a functioning fingerprint scanner. Where should I buy it from, though? I haven't been able to find any sites other than clove.co.uk, which looks kinda sketchy. Should I use Swappa or Ebay?

Thank you so much for responding!