Ben's place is really great! The location could not have been better. Just a few minutes walk to Notre Dame and plenty of Metro stops nearby. There are also a lot of restaurants close by which was very nice. If looking for a great croissant or baguette, you must go to Eric Kayser which is a short walk. The best baguette I have ever had! One thing that I should mention is that there is some street noise at night from the restaurants below. It did not bother me at all because I can sleep through almost anything and have slept in cities with a lot more noise (like New York City), but it is something to consider.
As you already know, this is a 5 floor walk-up. We did not pack light, and we managed to get our suitcases up the stairs with no problem. You only have to do this once, so don't worry too much about it unless you do not have the strength to carry your bags up that many stairs.
I highly recommend this apartment. The location is great!. The views out the windows are great! Everything was very clean and neat. It made our stay in Paris so much better than staying in a hotel.