Yeah the Steam process is pretty involved, I've set up the store page now though, it's in the review process and done a trailer (there's a link on this page to it), next steps are the polishing activities I'm going through right now and then removing any references to Patreon (Steam doesn't like those). Should have it up there in a few weeks if all goes to plan.
I've not heard great things from other devs about GOG tbh, maybe I've been listening to the wrong folks. Not ruling it out just yet but there are no plans at the moment.
You can find out the answers to those questions in chapters 5 and 6 that are out now :)