Hello, I was thinking of eventually studying some string theory and I came across Barton Zwiebach's book on the subject. Would this be a good place to start? I know some GR at the level of Schutz/Hartle, Schrodinger QM at the level of Griffiths, Classical Mechanics at the level of Marion & Thornton, and EM. However, I don't know any Heisenberg QM, QFT, or Group Theory. Would this be a problem in getting through Zwiebach's book? If so, can anyone recommend some books on the subjects I have listed?