Mackenzie - Consider a banquette running the full 10' length of the dining wall common to the bath, with a narrow pedestal / trestle table in line with the door - if the banquette is 18" (seat depth) + sloped back (8") = 26" wide, + table of 36" wide, you will have used only 5' of the 9' - you could even switch the left window and door, so that the corridor through the space was in line with the front door. You could go further to build the banquette at counter height and do the "table" as if it were a 6-7' long work island (some really casual people would put that on wheels) that serves 3 along both long sides - up to 8 with end "chairs" family meals, with several nice counter height swivel chairs with backs on the kitchen side to pull up to it when you do sit down to dine.

You could, of course, use the entire dining room area for kitchen, and move the dining to the sunroom, but if you want a larger kitchen and more open feel, I vote for a "fancier than usual" banquette. You can select a solid neutral microfiber fabric that looks like velvet but wears like iron, cleans up with a sponge. Depending on your style, you might tuft the back, and you can put deep drawers under the seat that pull out for things you might use seasonally. The banquette will gain you 2' in the overall room, and is ever so cozy for friends to hang out while you cook, or kids to sit and tell you about their day.

Opening the stairwell might lose your current coat closet but would make things more open. . .the current stair entry and exit is really messing up a more functional U shaped work triangle. If your budget allows you to flop the stair, and open it to the entry /living side, you could add 2' / take the entire backside of the stair wall of the kitchen for deep (put the new fridge there near the dining end) things, pantry storage, a full height wall - even put wall ovens (microwave over conventional oven) along that side of the kitchen. Then, you only need to locate the range top and the sink/dishwasher. Leaving them in the approximate same place as they are now would give you a very functional work triangle and save some dollars there.

With this approach, I might take most of the upper cabinets off the sunroom wall of the kitchen, perhaps adding some open shelves if your style fits that. The 2' you give up on the "non window" side of the kitchen won't feel like you've made the space any smaller - and 6' as the cockpit of a U shaped kitchen is big enough for three people to work comfortably - you could work out an armoire / closet at the end of the new casework to replace the coat closet.

If you aren't moving plumbing or vents, you can afford to switch the stair - starting at the living room end, and moving down and away instead of bringing all that traffic through the kitchen. You can reorganize your storage walls below to encompass Laundry and storage so you have a vestibule to the family room - this will lessen sound transfer from below to above as well.

Just some layout thoughts that should help you make progress. .