Apartment is absolutely as advertised - it’s a perfect size for a couple, and the balcony is a great size for lying out on. The location is fantastic for getting about Lisbon, within walking distance of many sights/restaurants/bars. Also highly recommend the restaurant directly below - Casa Dos Pecados.
Also yes the stairwell is very steep and we took very large luggage but if reasonably fit then it should be no problem.
Finally - when we booked we did have concerns regarding the comments about the neighbour below. We had no issues with her, and every night we came home after midnight, and walked up the stairs in a normal fashion, so i don’t believe she is over-sensitive, just be respectful of noise levels at night. I actually had a pleasant run-in with her when entering one afternoon, so don’t let a couple of reviews put you off!