both line and shimeji allow for official selling of icons/emotes. I would pay for it? I love the idea? Or will there be backgrounds or something? Any other kind of digital goods and merhc and stuff? I really really love this game I'm even working on a cosplay of Sherrlock Cohen, :)

Not sure about LINE or Shimeji stickers but Studio Élan's pretty consistent about offering merch & artbooks with their titles, and I doubt this will be an exception; nothing for Lock & Key yet but you can check out their store here:

Studio Élan Official Website (vnstudioelan.com)

Good luck with the cosplay!