I just want to clarify that this is the slab floor you're talking about and not something you are adding to a raised foundation? If that is right then it is a cheap solution and may be fun to do. Adding a laminate wood or carpet later is possible but in the case of wood laminate could result in the big chubby extra trim around the base moulding which a floor done by a good floor guy in the original buildout won't have to add.

I would suggest you take out the cabinet that is to the right of the stove and use it elsewhere in the house -- perhaps in the bathroom or dining room with a hutch above it. Then, I would suggest you have someone install a lazy susan cabinet in the corner between the sink counter and the stove, meaning you would move the stove down a bit and have a small cabinet/counter top to the right of the stove. I would suggest you have the cabinets refinished in white and then paint the walls a pastel you like. If you would prefer white walls, then add white-painted crown molding and paint the ceiling a light neutral blue, such as Sherwin Williams Niagara Falls Blue. Then, I would suggest you choose a favorite accent color and use this sparingly in accessories like towels, pot holders, small vases or floral arrangements, and a valence above the triple windows. For a genuine 1940s look, you might have white ceramic square tiles with a rectangular red border installed as a back splash behind and above the stove. If you are replacing counter tops, I would suggest a light color such as white with a beige or light grey vein or striation for some sort of pattern. You might be able to find the same color and design in floor tile OR opt for a wood floor as another poster suggested.

I found this photo online, perhaps it will help. In this picture the crown molding on the cabinets flow from the kitchen to the adjoining room. Maintaining continuity with the color and some of the trim detail will make the rooms transition nicely. Don't overlook the details like hardware finish, lighting and plumbing fixtures as these elements can also tie the two styles together. I hope this was helpful.

Heating sources here in New Zealand are typically Heat Pump or woodburner. I see a heat pump merely blowing dirt and dust/hair everywhere... keeping it in the air... and distributing it all over. I've run across this: www.thermaskirt.com which is very interesting. It's like a radiator, using hot water to heat, but on each of the walls, at floor (skirting) level. Since we have 3.3m (11ft) ceilings in this addition, it might be the most effective at providing heat where we need it without blowing dirt/dust around.