Seems like I am the contrarian. I think the look of the second rug is more to what you seem to be after. You don't seem to love the first one. The monotones are very soothing and it's really okay to have a monotone room, if that is what you like. Decorating is all about you. I like your inspiration picture with the second rug a lot. It's clean and that's what contemporary/modern is all about. The nice thing about a neutral room is that you can change it out when ever you want. If monotone is where your eye is going than my suggestion is you go with your eye. If you should choose to add color, something like the pillow attached would work with the 2nd rug as a color influence. It would bring in another texture. You can just pick any color in the pillow for vases and other accessories. I think the second mirror is more classic than the first. There is nothing wrong with the first as a matter of fact, I feel it has more of a wow factor but I also feel it will outdate itself. I would suggest a lamp with a ligher shade since the tables are dark. I am not sure I would go with silk drapes but once again, they will be fine to use. I just see something more casual in material like a heavy linen or something with gommets (did I spell that right?). Here is a link that might be useful: Pillows

how fun to be doing a refresh of your room. I am not a professional so I dont know the regulations and code for fireplaces, so i cant answer those types of questions. I do think though that I would keep your fireplace surround very simple. I say that because you also have to work with the 3 windows on the right and right now the fireplace seems to not quite work with those windows. I think part of it is the color, i would keep the wall color consistent with the rest of the room. the other idea is to just tile that corner and feasibly not have a mantel or hearth, just keep it simple. heres a few ideas. I will also say the way you approach the fireplace depends on the feel you want for the room in total. heres the concepts I was trying to explain

I’d leave the mantel (it has nice detail) paint it, the bricks and hearth black and then build a “Frame” over the mantel for the t. v. I like black t v’s on black walls.

Yes, thinset/board/thinset/board. Mix board thicknesses to get the desired height. As contrary as it sounds, cements don't always bond well to cured concrete. They make bonding agents that are applied to the cured concrete to help achieve a good bond: https://www.lowes.com/pd/QUIKRETE-1-Gallon-Masonry-Bonding-Agent/3521300?cm_mmc=shp--c--prd--bdm--ggl--LIA_BDM_210_Concrete-Block--3521300--0--0-_-0&ds_rl=1286981&gclid=EAIaIQobChMI5YqkuJic9AIVum1vBB2oJwVWEAQYASABEgLMsPD_BwE&gclsrc=aw.ds