Flavio's place is in an excellent location just off La Rambla. There are lots of amenities in the street itself too, like shops, restaurants and bike rental. It's close to metro stops also.
The flat was big enough for the two of us. While it arguably sleeps four (two single beds in a loft section), I think you would struggle for space in the living area with that many people.
Please note that the flat is at the top of the building and the climb is not easy. I'm a fit person but was breathing hard at the top! If you're unfit or have mobility issues this place most likely won't be suitable.
Flavio was great with communication, as was the manager, Ivan. We were able to chat easily by WhatsApp.
If you're looking for a cosy place close to La Rambla I'd definitely recommend it.