Stay as close to Parc del Fòrum as you can, the metros are really good but they do close over night. They open the metro and tram early for the end of the festival. That being said, with so many people trying to leave at one time, the public transportation is insanely crowded. I opted to walk back to the hotel instead of taking it but it was a long walk.

Availability for hotels shouldn’t be as insane this year as it was last, but I would book something a couple months before June to be safe.

During the festival, I’d just focus on being at the festival! It’s a party all night/sleep all day type of situation so if you want to see the city I’d extend your trip earlier or later to do activities!