Since you're changing the floor, I'd change the vanity and leave the tiled tub for now. Tiling a tub is a big expense, and it can be hidden behind a shower curtain. For the floor, you could use LVT, something like Armstrong Alterna or Congoleum Duraceramic. It's warmer and softer than ceramic tile and can be laid right over sheet vinyl and grouted for a ceramic tile look. You'd want tile to go under your vanity. Vanities have gotten taller. If yours is short, I'd replace it with a 34" H vanity. You could buy a sink base and three drawer cabinet from one of the RTA places. I'm most familiar with Barker Cabinets. If you want to keep the vanity, you could order new full overlay doors and drawer fronts from Barkers. You could paint the frame and purchase painted doors and drawer fronts. They offer a medium stain too. That way you can coordinate your counter, floor, and vanity color without being tied to the golden brown color scheme of the tile. I'd also cover that odd niche with a large mirror.

I would try moving the tub and vanity and put the tub across the back wall where the vanity is now and then the vanity could go where the tub is. BTW acrylic tubs are awesome , easy to manouver into reno spaces and so simple to keep clean.

I am attaching layout #3 with red/yellow rug. In this configuration, the exterior dimensions of the shower are a maximum of 42 X 54 inches, which gives me an interior of about 36 X 48 inches. There is a heating vent in the ceiling that would conflict with a wider shower. The shower pivot door needs to go on the lefthand side of the shower (to avoid conflict with entry door). This requires that the side wall (next to the toilet) be at least a 6" wide pony wall with glass above it hinged to the ceiling, and shower control valves on the inside of the pony wall. One aesthetic issue with layout #3 is that from the hallway, I would see a blank wall with no focal point. Either need to continue an interesting tile across this wall, add artwork, or move the window. The existing window is 21" wide and 42" high.

You say fixtures. I say faucets. That's what I didn't understand, so thanks for the pics. I would mix white vinegar and dish soap, 1:1 ratio, and apply with a Q-Tip or tooth brush. Let it sit for 15 minutes and see what wipes off. Of course that doesn't prevent it like a water softener would. Your pictures worry me a little. We're using black faucets in our remodeled BR, so I don't like seeing the spots on your bronze faucets. We've always had chrome faucets which are much harder to see spots on.