A quick response, If you're intimidated by a DIY visit, then, if for peace of mind alone, take a tour or two.
Intimidated? No. Overwhelmed by the all new experiences awaiting, quite possibly. My thought is that the tour, at SF or elsewhere, will provide more context, though maybe not having the flexibility of a self tour. That is the reason for my question.
However, while Barcelona is a large city (I didn't notice where you're from and "large" is relative), if you get a map of the city and understand the basic layout of the area, it is an easy city to get around in using public transportation. The Metro/subway is safe, clean and comprehensive in the area it serves, and the public buses are amazing. Get a Rick Steves book or Fodor/RoughRider/DK Eyewitness, etc. for Spain (specifically Barcelona would be better) and decide where you want to visit.
I have my trusty Europe Through the Backdoor book, and have been borrowing the latest edition of RS Spain. And lots of viewing online maps, including Google and Streetview. They've all provided much to understanding how Barcelona is laid out, and to help locate points of interest (to me), as well as transit stops. My mental mapping will tie that together.
Am a frequent user of the Metro in both Toronto and Montreal.
I'll post a new thread inquiring on guided or 'diy' tours. And another post for insights on the Feste de La Mercè happening during my visit.
John