As long as you have a copy of the files on the key, you can set up a new key, and on first boot it will walk you through transferring the license to that new key. You can do that once a year automatically through the Limetech servers, if you mess up a key before the year is up you would need to talk directly to support and explain what happened, and they can manually transfer the license.
Yes, the data and pool disks are all standard linux formats, currently either XFS or BTRFS, so any OS capable of mounting and reading those file systems can access the data.