La Merce for my honeymoon

Hello to the beautiful country of Spain and Reddit,

My wife and I are thinking about going to Venice/Barcelona around the time of La Mercè. If we are in our mid 30s, what can we expect? We love good food and concerts and La Mercè seems perfect on paper. We’ve been to multiple festivals (punk, edm, etc) together and are passable in Spanish/Catalan (working on it full time before we go). We were hoping also to see La Sagrada Família while we were there so we were thinking of buying tickets soon.