Temporary bookcase units until budget allows for “built-ins”.

do you need the built in storage? Clear off the mantle, and mount the tv to the left of the FP keep it simple, the sone is a statement in itself.

Get 2 caninets the same size one for each side of the FP wall mount the TV above one at the proper viewing height ( center of screenat eye level when seated ) This means the cabinets will not be very high then add a large piece of art above the other to balance the TV and yyou are done. Noshelves filled with a buch of stuff that never needed to be dispalyed . If you have stuff that should be dispalyed then you can do shelving Mount the TV on an articulating arm for viewing .

Beautiful room! Get rid of the ladder thing. mount the TV on one side at seated eye level with a long low console underneath. Consider removing all the little doodads from the area for a clean modern look.

Do you need built-ins for storage? Will you share a photo that shows the whole room?

You don't need to fill the area around the fireplace with a built-in. You can make the spot look more finished with large art, a comfy chair, a plant, a floor lamp, etc.

Built-ins never look good with these types of stone fireplaces. Your space has too many elements controlling the height & then the shelves will extend beyond the stone. Never a good look.

Built ins that look good have the fireplace extend out in front of the shelves and cabinets like you see below. You don't have that condition.

You can place chests on either side with art above.