Gorgeous house. Nice kitchen, too many uppers for me though. ;) I love the screen, I dream of having something like that in my home one day. I don't think I'd be drawn to the chandelier on its own, but I do think it looks lovely and appropriate in this home. I like the mix of contrasting light and dark tones, and the geometric sqare/circle shape. Okay, now I'm wondering why I initially didn't appreciate the pic of the chandelier on its own, as I like the parts of it very much. A natural knee jerk reaction against brutalism maybe.

Another tour I did was of the Gamble House in Pasadena. Interior photography also forbidden, of course. Some interior photos available here. The only Greene & Greene house open to the public (they claim) the house is an impressive example of the pinnacle of the arts and crafts style - and what happens when an unlimited budget meets very exacting craftsmen. Although only built 10-15 years before Hollyhock House, and also influenced by Japanese architecture, it might as well be in another world. Our docent sniffed that "unlike Frank Lloyd Wright", the Greenes had incredible attention to detail. Hearth inlays match wood, silver or semiprecious stone inlays in the furniture. Mrs. Gamble's writing desk has an inlay to match her favorite Tiffany vase. Each room features one type of wood, even to the windowsills. Each door is custom designed to match the pattern of panelling in the room to which it belongs. The butler's pantry has a custom cabinet to store table leaves... The table, of course, designed by the Greenes. The carpets were also designed by the Greenes and were surprisingly modern, largely plainish with subtle edge patterns. The house is panelled nearly floor to ceiling and they light it with era-appropriate 15 Watt bulbs, so it is extremely dark. I found the style impressive but also a little oppressive. It was dark and...well, being an almost 100 pure expression of the Greenes' style, very formal, very regular, very matchy. Here are some details from the foyer- exposed pegs, straps (decorative but giving the impression the stairs are strapped together), the exposed underside of the stairs (showing the bones of the house in arts & crafts style), the section of banister carved from one enormouse piece of Burmese teak, and the stained glass front door which has two identical layers of stained and leaded glass.

I don't think it's a matter of affecting historical significance so much as creating a bathroom that looks compatible with the house long-term. The original bathroom will always look "correct" in a house, no matter how old it is, because it's what the house came with. Replacements can be problematic. I doubt the people who put the remodeled baths in the FLW houses I've shown above thought they looked as out of place in the 1980s or 1990s or early 2000s as they look out of place now. Everything about the bath the OP has pictured says "original". Often the toilets got replaced, but that tile-in sink, faucet, the vertical tube lighting, and the Hall-Mack recessed soap dish, cup/toothbrush holder (which you can sell on eBay--a new-old-stock one is listed for $175), speak to the era of the house. I don't think the OP has to recreate the original bath, but the closer in spirit the bath is to the original house, the less likely it will look dated and out of place in seven years. It might still look dated (like the original looks dated) but not out of place, so much. I really would not use any tile that is trendy enough to say 2010s for example.

The interior concrete wall are painted a yellowish beige- i would like to bring in a grey but worry that the grey will add to to "cool" - Any recommendations on paint color options? I will be putting in a room size area rug and pottery barn turner large leather couches and chairs. Do not do gray. It does not go with the feeling of the house at all. I do like eam's suggestion of taupe. The kitchen -while in fantastic condition, I feel needs updating and some better visual design by bringing in taller cabinets - I disagree because it will destroy the horizontal line going on in the kitchen. The whole idea of the FLW homes was low to the ground and giving a horizontal (not vertical) feel. What I would do instead is redo the cabinets but make all the lowers wide drawers so you have more room to store stuff inside. I do not want craftsman style and do not want current day modern- i think the simplicity of mcm plain fronts in a lighter wood may be good. But can not find a good source (even inspiration pics) any suggestions? See if you can find a good KD to help you. I will be hiring an architect to design the addition of a master bath and a deck on the back- but if anyone has suggestions or pics of other FLW with additions it would be great! I am seeking interior inspiration for design finishes that retain FLW style (perhaps a tending towards Japanese?) I would repeat the finishes you already have in the house. Why try and reinvent the wheel?