However, for the auto-updater part, I don't think Orbit is functioning correctly: Every 10 seconds, it is hitting my HTTP server (where I am hosting the updated binaries and the corresponding meta-data) and my HTTP-server is returning HTTP 400, most probably because my HTTP-server is not able to understand the request-data. Can someone please let me know if I need to configure anything specific on my HTTP server?

The self-hosted updates functionality requires a paid Fleet license. Let me know if you'd like to be connected to our sales team to see about getting a license -- licenses come with guaranteed support to get you up-and-running with the autoupdates and any other support needs you have.