Ok usually one to say to slap that molding on every single wall lol. But I don’t think your room will NEED it after the shiplap and that’s why I’d recommend waiting on that. Wait till the space is complete with what you have so far and then we can decide if wallpaper, molding on the bottom Half of the wall, full molding wall.... is necessary... if you just want it done then I’d do some molding but if your ok to wait. Wait! Love this space. Love the decision to keep the stairs open. I totally see your vibe from the raw house you have!! It’ll look so amazing so soon. Can’t wait to see!

Just keep in mind that rarely will you ever see both areas directly straight on so the difference in size won't be as noticeable from an angle. You'll know the difference is there, but most won't notice particularly if you use shelves. If you use cabinets then the key would be to use different size cabinets so any fillers are the same size on both sides. Again you will know the sizes are different, but unless someone is looking for that in particular it won't be very noticeable. Either way this is something that could be done at a later time even after you're done building if you just want to wait and see if you feel you need it once the FP is finished.