The goal is ideally to “lift n shift” but that’s not possible with amazon lightsail since one cannot import an existing image. So yes it would be using the exact same S3.
It seems like your approach is closest to lift n shift. If I understand what you’re saying, I can just tar/gz the entire /var/discourse folder from the original server and untar it into the new server followed by a discourse start and then just repoint the DNS to the bee server. Is that it? Do I need to rebuild discourse in the new server? What about Nginx, docker and other dependencies outside the folder?