This is a great location in the heart of Paris. It's just a short walk to Notre Dame and St. Chapelle. You are a few blocks to the Ponte Marie Metro station as well, so it's relatively easy to get almost anywhere in the city from there.
The apartment would be comfortable for four, or maybe 5 if someone wanted to sleep on the couch. The 4 flights of stairs aren't easy, especially with a heavy bag. I'd say this place is more ideal for two younger couples or a young couple with two children.
The apartment has a washer and dryer, dishwasher, range, coffee maker, and hair dryer. The kitchen is tight, but would be okay for simple meals. It comes with all the pots, pans, and utensils you might need. The refrigerator is small and is in an awkward spot, not easy to get things in and out. There is no air conditioning, but the weather in late July was very cool in the evening, so open windows worked fine. There are also a couple fans if you needed them.
We had to buy toilette paper, dish soap, and laundry detergent, but there was a small market down the street that had all the necessities. Across the street from the market is a very nice pastry shop, as well as a well stocked cheese shop.
Everything was clean and organized. The apartment has windows that open on a nice courtyard. It is surrounded by other apartment buildings, and noise at night was generally not bad at all even with the windows open.