Paolo & Franziska's place was just as described and true to the photos. It was also near to some excellent cafes and restaurants. I found the location excellent for sightseeing too!
The stairs were not an issue for us day to day (only about 3 -4 short to medium flights of steps) - we actually preferred the exercise after a day of eating goodies in Rome. For those with suitcases and worried about the stairs, as a gauge, a small to medium sized woman should be ok lifting a 24- 25kg piece of luggage when going up or down.