I have a similar angled fireplace. If you're not wedded to the TV over the fireplace, I would suggest putting it next to the fireplace and angling your furniture around the TV. That's the way mine is. You can see the TV face on from some pieces of furniture, and the fireplace face on from others, but all can see the TV and fireplace. I use my fireplace daily in the winter so don't want a TV over it, it gets too hot up there. I would advice against a sectional. You can get the utility of a sectional from a couch and a lounge chair or two. I'd be more apt to angle the couch where the chairs are in your picture. A floor drawing would probably help with furniture placement. I think you could totally redo the room to match your inspiration picture, keeping the wall color unless you really want a dramatic change. I love the curtains in the inspiration photo! Your house is open concept like mine. Hard to figure out whether to repaint or not, because once you start with one room, it snowballs to how that affects the other rooms. You could always do one wall another color like the current owners have in the photo. Wish I knew what that color was in your inspiration photo. Browns and tans are the worst for me as far as choosing the right one. I burned up a lot of cash in sample paints when I moved into my new house. But it is the right time to repaint, before you move all the furniture in . . .

My fireplace is about the same color rock as your's, and I have the same type of rock mantel! It was hard finding just the right things to put on it because it's in a dark corner. Light is key, do you have a narrow lamp you can set on it? The color that pops for me is cream. For awhile I put my small collection of crocks on it and the color really stood out. Now I have a largish picture sitting on the mantel leaning back against the wall, with only one thing on either side of it, one being a lamp, even though there's an overhead spotlight which I sometimes use. When you set a lot of small things on the mantel, along with the dark clock, it all gets lost. It takes a lot of work decorating a mantel, something I thought would be easy. :) I'll try to find a picture of my mantel tomorrow.

If you google "faux fireplace" there's lots of ideas on how to use it without an actual firebox, if that's what you're thinking. Here is a Candice Olson design where she used a mirror and candles, but I think it would be even better with an antique surround.

I wanted to do a seating area with two chairs on each side but not sure if it will look good. these walls are not fully perpendicular so makes it tricky to decorate the walls. Any ideas on how to decorate this odd office corner space??