Have you discovered remarkable.guide yet? Your issues lost says there is no documentation about what to do after getting SSH access, and that you have started your site for documenting that. I think that remarkable.guide may help answer some of what you are looking for.

https://remarkable.guide/guide/access/ssh.html

There is no download link, you run a command over SSH on the device itself. It will download and install the correct patches for your OS version.