Alejandro is a very responsive host and helps you with his guide that will be attached to your reservation with many recommendations of restaurants and so on.
The apartment is on the smaller side, (it is in the city after all) but for me it was all I needed, clean and tidy with pretty much all you might need. Kitchen is well stocked.
Don't forget your own spices and maybe a few other things you don't want to get in big quantities if you are planning to cook. There is a big supermarket very close by though.
It was my first time in Barcelona. I felt fine walking to many places, some very close by and using public transportation if needed.