IMO, the cabs and furniture need to coordinate, but not necessarily match. For example, we have white perimeter cabinets in the kitchen with merlot colored hood & island. Kitchen is open to family room with 2 built-ins in a slightly off white color. Cubbies are just around the corner from kitchen and can be seen through the doorway--they are also slightly off white. There is enough distance between the whites that you don't notice they don't match--they just coordinate. Our master bedroom furniture has a mahogany finish with antiqued gold pulls, the master bath has espresso vanities with antique pewter pulls and you can see from one room into the other. Again, they are just far enough apart that you really don't notice the difference & they coordinate. Stained furniture can be coordinated with painted vanities/cabinets & vice versa. Unless you're planning something totally outlandish, I think you'll be just fine. Hope this helps!

I think it will be stunning in the cognac. I'd do it in a heartbeat and I love all your choices.

No, I would not paint a bathroom in a home I'm trying to sell black. That is too specific to appeal to the masses (which is your target audience). Could a designer make black walls look amazing? Yes. Can people on this forum send you pictures of bathrooms with black walls? Yes, But none of that relates to you because you're not a designer and "most" people will probably not respond positively to that. Yes, your bathroom is very dated. But what I would do is start with A) a budget, and B) an overall plan. Get someone with some decorating sense to help you BEFORE you do anything. There are too many things wrong in that space to start calling it all out without knowing how much money you have to spend on this and the style of the home, but in general if you can't remove that paneling then you're looking at painting it a light, neutral color. You're looking at painting all of that cabinetry and trim. You're looking at a new counter top and sinks. You will need new mirrors (you need two, one over each sink), new lighting fixtures and new faucets and cabinet hardware. And then you're going to have to remove that weird angled wall piece, I'm not sure what that is actually, but it has to be removed.

The tile in the picture w/the tile you posted? no. post all the tiles you plan on using. a gray porcelain tile doesn't tell me anything. and gray and that yellow one you posted, will not work. don't mix linear tiles and stay away from wood-look anything. the chevron one in your picture is ok, but look what it's paired with. white tile platform and a marble look tile. that's it. no other linear tiles. It's a very busy patterned bathroom. it works because everything else in that room is plain white or solid wood laminate. no other patterns, or busy looking vanities. it's wide open so the eye can roam. can you imagine another linear tile along the tub platform?Or a vanity with curves or other designs? If you like that bathroom, then copy it. exactly. otherwise, it's not going to look anything like it.