Hey, is it possible to use the Advanced Sessions plugin to connect to steam and have friends join created sessions using steam without uploading the game to steam?
If you want to use steamworks in production, you will need an id, which you will only receive after a project review.
You can find more information about the review process here: Review Process (Steamworks Documentation)
But you can use the development global id (480) and run steamworks from anywhere, even if the game is not packaged yet. There shall be limitations about the use of this id, but I guess it will work very well for sessions finding.