How high is the knee wall? You're going to have a window in that knee wall? Dormer or low-set? What is the ceiling height over there? Would a skylight work instead? Why do you prefer not to have the window over sink or shower? I think all of your sketches tend to chop up your space. To have to pass the shower walls on your way to the sink or toilet is rather confining. Usually it's better not to put plumbing in an exterior wall, and it's nearly always cheaper to keep it one wall. My instinct would be to put the sink on the left wall opposite the door, as it the pleasantest part of a bathroom to see when you walk in or the door is left open. Then the toilet next to it. A sink should have 30 inches of wall space and a toilet 32 inches - but I am not sure if that space can overlap in the unoccupied part of the wall - I think it can. And then you are left with the space next to the exterior wall. You could have a big shower the whole width of that wall and a window set high in that wall (or a skylight). Or a smaller shower with the window next to it and shelves or vanity table or chair under the window. You can have frameless glass doors which will keep the visual space open, or even a partial partition and doorless shower - you put the showerhead in the partial partition aimed away from the shower opening. Or you could have a tub with a hand held shower. What you do with that exterior wall depends a lot on your climate, and how high that knee wall is.

I believe your measurements are in millimeters not centimeters so it is 7x9.4 ft. Not a small bath but not quite large enough to to house all your wishes and maintain function and a feeling of space. if you want a double tap vanity I think you need to go smaller with the tub to make space. Or if the heat exchange works out maybe heat with radiant floors and lose the radiator to make more wall space for a larger sink. Now if your measurements are truly in CMs than 70x90 ft is large enough to house ten of everything. ;)

Mix of metals doesn't seem worth worrying about -- that's pretty common these days. I might turn the light fixture to face down, but just because it seems unnaturally high. For the corner/mirror, I think I'd try to find a nice wall cabinet that could go in that space, to act as a linen closet and give you a bit of a more intentional-looking solution. It's probably ok to block that wall switch if it's a duplicate of controls you have elsewhere, but you have to stay slim enough to avoid the window. Ikea has the right kind of thing. (Most of their explicitly bathroom cabinets are tall and narrow, but you could use one of the other bookcase/door/basket systems to the same end.) Otherwise, you can't do much to make it less brown, other than by putting in some colorful rugs and towels with art to match. It's possible that the paint could be a bit cooler, and I suppose you could paint the vanity from red-brown to white, with some effort. But really, this is a perfectly nice bathroom that just isn't to your style. Dress it up in things that feel more like you and then don't worry about it for a while.

If you're redoing the shower anyway (looks like tile and grout are degraded and may not be keeping moisture out of the wall), then a tub is pretty cheap, and you might be glad you replaced it rather than having to build your whole bathroom around the current shade of gray. Plus, it may look even worse once the rest of the room is fresh and new.