I don't have a picture (I can grab get one if you like), but I did the same thing in my current project - new wood floor in the kitchen going right into existing in the dining room. The floor installer feathered some of the new boards into the dining room floor so it looked continuous, then I had all the existing floors sanded and refinished and stained the old+new 1 color. The result is a transition that looks completely continuous and uniform. Of course I had to refinish all my existing floors to do it. If you don't want to do that the only thing I can imagine working is a perpendicular strip to edge the new and old. It'd be impossible to match the old stain with new perfectly so you'd need something to separate the two. I have a spot in my house where the boards are mismatched so whomever installed it back in the day put a strip. I attached a picture of that.

Your floors will never look like they belong together...one is a site finished product and one is a factory finished one. They will complement one another maybe, but the two 'types' will definitely be noticed...but probably only by a professsional wood person or an interior designer. A plank, saddle or a decorative transition (piece with inlays or designs)...something like that will help seperate the two floors and make any disimilarity less noticeable.

Thanks SJ McCarthy! Given what you said about the original floor (oil based finish - I think they are Swedish finish from what I one time heard from the listing agent - and no stain), what would be a good selection for factory pre-finished floor? The purpose is to lay down the new floor for now in the carpeted area and make sure they don't look too different or visually unacceptable. You also mentioned that the natural break (doorways and breezeways) will help my change, which I assume it means the natural breaks will make the mismatch between floor area less obvious. I think they are plainsawn from the pattern, red oak, so going for something like a natural red oak from say Bruce with same strip width would be OK? Or what color would be best to match the Swedish stain? I take what you said "Even a factory finished solid red oak floor can be refinished like the floors you already have. It makes it easier in the future to get them all the same colour/finish." as that I can refinish everything in the future (e.g. 15 years down the road) to get them all aligned in finish and color if I want to. I am also planning to install the hardwood floor in second floor. Since they are at different floors, do I better off use the same species/stain/finish of wood for second floor? If so, can I go with a wider plank (say 3 1/4" or 5")?

Why do you want to change the kitchen flooring you have now? I see it in the photo above where you ask about shelving, and in the one with your dog. It looks fine with the adjacent flooring. It will look good with white cabinetry. As to your question about shelving, that is really a kitchen layout question. You can post on the Kitchens Forum asking for layout help for your renovation. But you will need to provide a drawing of the space with measurements. It does not have to be fancy, a handwritten pencil drawing will do, if it has measurements and shows openings. Houzz Kitchens Forum