Web3 became a marketing term, doesn't even really have a clear meaning, but it's used as a catch-all word for blockchain-related things like NFTs, cryptocurrency projects, etc. But most of those are not truly decentralized, whereas Lemmy and other fediverse projects are.

In addition to what's been said already - the community-specific wikis and megathreads. The amount of information I could find there about sometimes very niche topics was amazing. Hopefully something similar will be possible with Lemmy.

Yes. To add to this, if an instance suddenly changes its rules (e.g. in response to the influx of new users), I have to either adhere to those rules, or abandon my old account. I think allowing migration should be a priority.