Sounds awesome! I don't think you need to worry that much about the content amount on Steam. It's great that you're adding content to differentiate it from the jam version, but if you compare it to popular small games like Reigns, Clickyland, Florence or Stacklands, your game isn't lacking.
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Right! I'm pretty pumped right now and I'm gonna go for Steam! I'll keep working on it for a couple months I think. I actually don't know how long I should give myself for this game haha, and probably the hard question will be when to stop and just launch it on Steam. Hopefully this post ages well :D