I, too, can appreciate shiplap - but it doesn't match the style of your home, especially if you are adding crown molding! Honor the home's style - it's beautiful as is. Paint all the walls one color, white ceilings (or a very light mixture of the wall paint color).

I suspect the paneling above that appears to be on an angle, is a bulk head for something, and I would be very cautious, trying to remove it. It may hold plumbing pipes, or it may hold ac vent pipes, etc. I would paint the walls all to match, but, leave the wood on the slanted ceiling part. I would paint the bookcases white too (different sheen, but, same color white as the walls), but leave the mantle like it is.

It's too bad you aren't interested in redoing the fireplace w/tile. (when that fireplace was built, it was built w/a wall. leaving it as is is not the best design choice. It's very heavy and bulky looking in the middle of the room. Let me show you some options that you may not have considered.) Jasmine Roth did one just like that and it came out spectacular https://www.jasmine-roth.com/hidden-potential/help-i-wrecked-my-house-season-1-episode-4/ I would copy this in a heartbeat. trimming off the sides, creating more of a flat front,, makes it a focal point but not in a over-powering way. you mentioned a slate/blue-gray. You could do this tile on the lower portion, or the entire thing. it's stunning Bring in your color w/art, or a bright sofa, pillows, etc. If you like the white brick, consider getting a solid beam for the mantle and try decorating it like these photos You could get some thick basalt tiles and do those for your hearth (or a remnant black granite piece) stage your furniture like shown here, along w/the fireiplace decor I love this one. redo it w/black Zellige tiles surrounded w/white walls/ceiling, and some great furniture. does this look like a black hole? of course not. it's gorgeous. use any color you like Blue Zellige? Aqua? I love this tile. When surrounded by coordinating colors, it's beautiful. here's your teal zellige. something like this all the way up in a herringbone would be amazing. you could even close off one side, or, do an attached built in shelving (similar to this) on one side. another alternative, you can stucco or use a roman clay right over the brick and paint. around the hearth do a cement overlay and polish until the aggregate comes through.

Is it your home? If so, you can cut a piece of the paint out (about the size of a quarter) and take it to Sherwin Williams and they will match it. MUCH better than trying to figure it out from a picture. I use the color snap app frequently and it usually does not match the pictures well - it just gives you a vague idea.