Will you have them added in time for the launch? https://github.com/Facepunch/Facepunch.Steamworks or https://github.com/rlabrecque/Steamworks.NET are good frameworks to easily support them.

I couldn't find a button on the main menu for leaving the game once I was finished playing - is it missing, or did I miss something?

Any chance you can add a button to skip gameplay/puzzles? Or just a setting? The writing looks very interesting :)