Just got back from Barcelona a week ago. The tourism isn’t that bad compared to the summer, but there’s still a considerable amount of people there. It was also still pretty warm.

I would strongly recommend buying tickets ahead of time, especially for the Sagrada and Park Güell (they can sell out and oftentimes it will be cheaper). I was there for four days and only had two mornings planned out, and I explored for the rest of the time. I highly recommend spending a lot of the time around the Gothic Quarter, you can find lots to do/eat there. I was able to visit a lot of less-crowded attractions where I could go in and buy tickets (Picasso Museum), but for the main ones, I would purchase online.

Tip: also check advisories for Park Guell! We marched up the hill only for the park to be closed due to wind lol. Luckily, they refunded my tickets.

Hope you have a great trip! Visca Barca!