Nothing really only telemetry is send to n8n but you can turn this off.
Everything is stored locally in the database you configured or the sqlite database that is included in the docker container (so attach a volume for that) if you do not set any database options.
then you can reset your account via a CLI command.
Point 3) was meant differently. What if “n8n.io” disappears or block my account for some reason? Can I still use me work after that or the the local installed software blocked?