Well, first of all - remember, that Tails is Linux by heart, so - basically - there's an attack vector for gaining access to all the hard drives attached. If you want true anonymity - unplug it when you're using Tails : physically or via BIOS. Where to save data - it's totally up to you: Tails is Linux, so just mount it and use it
It's decentralized in significantly different fashion than .crypto domain.
In blockchain-backed domain system you can claim any name not claimed by anyone else. In .onion all you can do is to generate new private key that maps to SOME domain name (hash of your key). Period. Unless nobody else knows your private key, nobody else can publish hidden-service on ...
DH key exchange is totally unrelated to the IP hiding mechanism - it's for point to point privacy. The IP is hidden because when the 3-layer tunnel is built - the "onion" - it is built one layer through another, so the third chain member will not be able to see your IP because you will talk to it through a second chain member you're talking to ...
Yes. You will probably want to see these two blog posts:
Well, it looks like they're using a Cloudflare or a similar service to do tor blocking and CDN service. They do track you as you're using their service, so - discard them, there's nothing more you can do from your side