Alex was very helpful and was at the apartment before us.
The apartment was as described and was comfortable for two adults and 4 children (aged 3, 8, 11 and 15). They loved it and nobody ever mentioned the 4 flights of stairs. WIFI is good and TV is a Smart TV so "online" viewing was very easy.
Location was great. Close to Metro which will leave you anywhere in the city. Walking distance to Marina, La Ramblas, shopping and plenty of bars and restaurants.
Felt very safe in that neighbourhood - even late at night. There is a bakery next door where I got my breakfast every morning. Beautiful croissants and pastries and a decent coffee at a very cheap price.
Small supermarket 30/40 yards away with all minor necessities available. Nice pedestrian street 100 yards away with plenty of bars and restaurants if you want quick and easy food/drink.
Had a great holiday and would definitely go back. Staying in this apartment is far cheaper for family of six than staying in a hotel - and I think it was far more enjoyable than staying in a hotel anyway - the children referred to it as their "cool house" and did not want to go home! Thank you Henri