I'd say Sergi is very reliable, everything concerning the organization of our stay and our leave worked without any problems. The flat is very comfortable, clean and modern. The bathroom and the kitchen are quite new too and the dishwasher and the washing machine are a real luxury.
Gracia is a very authenticly spanish part of Barcelona, which is still located perfectly central within the city. You can do and find a lot by walking because the big shopping street Passeig de Gracia is very close. And the Passeig the Catalunya and the Sagrada Familia are also interesting for tourists and not too far away. We would also recommend to walk through Gracia some more at night. There are a lot of plazas where you can just sit down with a beer and sometimes you run across a free concert or some other cultural event.