Yes, you can do that. The bath bar style is fine but if you choose a vanity light, a two-light fixture is better with a 60" vanity. A four-light fixture is enough light if you want to use just one light above the mirror.

Flo - do you offer e-design services? would love to work with you on another project that is making me cross-eyed! We were working with a design firm and that was a disaster - first designer fired by the firm, second one started off incredible and then disappeared and we're with two unfinished jobs. I like your design esthetic and should be easy enough to do remotely :)

Painting that wall a dark colour will reduce the contrast between the fireplace and the wall, and help it look more balanced in the room. I suggest a very dark version of the green on the other walls. It would be helpful if you took some more close up pictures of the mantle. Is it wood or the same tile? Krylon high-heat enamel comes in a copper colour. Just spray paint your fireplace tools and screen for a quick inexpensive fix. Or, say goodbye to that black tile, and tile over it. You won't have potential water issues that people warn about when doing this in a bathroom or kitchen. Someone in another thread used stick-on tile to go over a row of decorative tiles above their bathroom vanity. Lots of how-to on the internet. If you're not a do-it-yourselfer, it's a small job for a tile pro or handyman because there's no demolition or drywall work. https://www.bobvila.com/articles/can-you-tile-over-tile/ If the sides of the tiles show, just paint them your new tile colour. I painted the tile edges in my bathroom and it's lasted 20 years. Or, paint the tiles. They get no wear and no moisture. Lots of how-tos on the internet. https://simply2moms.com/how-to-paint-a-marble-fireplace-with-chalk-paint/ The row of tiles above the mantle should be painted the same colour as the wall. You can buy or make a slip cover mantle (or mantle cap or mantle cover) that goes right over the existing one. No demo required. https://www.homedepot.com/b/Fireplace-Mantel-Cap/N-5yc1vZ1z10hgv This might be too country a look for you but a burlap mantle scarf would break up the sea of black. I wouldn't leave long fringes because of your cats. https://www.pinterest.ca/pin/280771357990481981/

Have you considered molding? It would draw the eye upward to help balance windows and a large chandelier will help as well. Then you need only decorate mantle and a layered look would feel more substantial. Just adding art or a mirror may feel lost, with the height, but it‘s hard to tell without seeing the complete wall.