This apartment is great if you don't want to spend much time in the communal space. All fittings are Super cool and the bathroom has a fantastic shower. There is some noise from starting planes but I guess you will have that in most places in Lisbon.
The flat is stylish and perfectly located between Belem and Lisbon with easy connections by public transport.
The living room faces a court yard and feels a little like you are sitting in a shoebox but otherwise everything is super nice.
I think the stairs are no problem unless you are extremely unfit or have difficulties walking. 3rd floor walk up.