I always ask my clients what they plan to put in the built ins . I find many times they have no plan just think they need shelves beside the FP. I sure hop you are not putting a TV above the FP since you have great wall space for that . I like simple low cabinets on either side of a FP with the TV wall mounted on an articulating arm on one side above the cabinet at the right height and a nice piece of aret above the other cabinet to match the TV height Then some simple mantel decor . If you have special things that need display then you do shelves to fit those things and I think your inspo pic is a great example of nothing worth displaying just filling shelves

The balance is fine, but it looks like your furniture is modern, therefore suggest a more seamless fireplace and even staining vs painting.

You win the gold medal for "technicality in applying tape" - it is very precise.

There's some things to work out that may affect proportions slightly, like the transition at the top of the fireplace ("mantel" area) and the depth of shelving vs applied front to FP, and how depth affects window, etc.

Is the rectangle above the fireplace a tv or picture? If it’s a tv it’s too high and pretty small by todays standards.

Thanks all for your feedback. Mainly I guess I’m hoping that the depth of the shelves and mantle don’t consume a portion of the room. You can also ignore the furniture in the room.