cincsentits will do a grand tasting menu if you give them 24 hours notice. It can be booked from their website. Do not miss Alkimia when in Barca it is superb check out flickr for a pictures of the tasting menu.
Generally, Spain is very informal. Even in Arzak and Sant Pau, very few diners are in jackets and ties and that is in the evening. Sharp casual would be fine. Same for Cinc Sentits. I am envious...have a great trip. Please report back.