Some popular choices for beginners include "Quantum Field Theory for the Gifted Amateur" by Tom Lancaster and Stephen J. Blundell, "Quantum Field Theory in a Nutshell" by A. Zee, and "An Introduction to Quantum Field Theory" by Michael E. Peskin and Daniel V. Schroeder.
For advanced students, "Quantum Field Theory" by Claude Itzykson and Jean-Bernard Zuber, "Advanced Quantum Mechanics: Materials and Photons" by Rainer Dick, "The Quantum Theory of Fields" by Steven Weinberg, and "Introduction to Quantum Field Theory" by Luis Alvarez-Gaume and Miguel A. Vazquez-Mozo are popular choices.
Yes, "Quantum Field Theory: A Tourist Guide for Mathematicians" by Gerald Folland, "Quantum Field Theory Demystified" by David McMahon, and "Quantum Field Theory for Mathematicians" by Robin Ticciati are commonly used for self-study purposes.
For a more mathematically rigorous approach, "Quantum Field Theory and the Standard Model" by Matthew Schwartz, "Quantum Field Theory" by Mark Srednicki, and "Quantum Field Theory: The Why, What and How" by Thanu Padmanabhan are highly recommended.
Yes, there are many online lectures and notes available for free, such as the QFT lectures by Leonard Susskind, the QFT course by David Tong, and the QFT notes by John Preskill. There are also online forums and discussion boards where students can ask questions and receive help from other learners.