These chairs are easy to recover and the range of fabric available today gives you plenty of choice. I say go for it. If you don't feel up to it yourself get an upholsterer, but plenty of YouTube tutorials about.

Something to take into cosideration would be the amount of light you have coming into the bathroom. Obviously if you have considerable light and air the tile shade wouldn't be too much of an issue. On the other hand if the room is small and not very light filled, then the lighter shades would be preferable giving the illusion of making the room appear bigger and lighter.

Once you go white (which I think is a great idea) you might find that the existing handles look good. If you want to change them I would suggest handles that are consistent with the period of the house/kitchen. And, I would keep them simple based on the design of the cabinetry. :-)

I have just bought a schweigen with motor on the roof. The best information and help that I got was from the installers. Parex Industries are the NZ importers, but I must say the only help they gave me was the phone number of the installers. I just tried to find it for you but can't. They are brilliant to talk to and get advise from. I spoke to them before I purchased. The one thing that I realized is the installation is one of the major factors. Give Parex a ring and get installers number will be your best bet, all the retail outlets did was provide conflicting information.