I would suggest not installing a double hung window (up and down type). It would be difficult to reach over the counter to open it. With the measurement you provided an awning window would be something to consider. It opens out at the bottom. The crank is located at the bottom and the locking levers are located lower on the sides. Both the crank and locking levers are easy to reach. Over my sink I installed a 40 inch wide by 30 inch high awning window with an 18 inch fixed transom window above (attached to) the awning window. The total size is 40 inches x 48 inches. The fixed transom window has vertical muntins which match the style of my other windows. I used Marvin windows. Marvin has many style options.

We solved our problem in a way I've never seen done before...we contoured the window sill around the faucet. We call it our "custom" window sill!!!

I would use a 60" wide x 40" high picture window with a 20" high RO operable transom above it. Then you could use the transom for ventilation and not have screens on the lower window. The wall above the transom would be about 7" tall, enough for trim and a ceiling molding. A structural header could be substituted for the second floor band joist/rim board. I've done it many times.

I came upon a similar predicament in this home two years ago. The original window above the sink was exactly like yours. Except wider, and for some reason had been painted shut! Almost every window in the home had a lovely half arch accent above each one, so I went on a search for an arched-styled window to replace the original eyesore sitting above the sink! Not only were standard arched windows very expensive, they took months to deliver. So I spent about three weekends scouring second hand shops, resellers and Habitat for Humanity Second Chance stores. Finally I came across a large warehouse where they deconstruct old buildings and homes, then sell every salvageable material imaginable. There I was able to find a gorgeous arched window in its original wood frame with trim, and walked out with it at the pretty tune of only $65! We stripped off all the old paint on the frame and trim. Cleaned the glass well and then my carpenter blocked in the surround wall so that we had a new custom opening for this (old) arched window. Added new drywall, a tile trim accent to the arch to give it more impact, and a quartz windowsill...plus two new gooseneck light fixtures above...and it became the focal point in the kitchen! It also gave such a magnificent view of the new sunroom and deeply wooded back yard beyond. Although it was a custom job, it did not have a “custom window” price tag. My point is to think outside the box, look around your home for inspiration (other key structural accents you can copy or find a likeness), and always check around for off-brand, and in second hand and resale warehouses and suppliers when it comes to a unique or challenging window, door or space. Don’t give up!