Quantum Field Theory is really just ordinary Quantum Mechanics. It is necessary to use fields instead of "wave equations" because the number of particles can vary when the energy of a system exceeds a certain threshhold. (e.g. a single photon having an energy equal to or higher than the E=mc^2 energy of two electrons can transmute into an electron-positron pair. 1 particle transforms into 2. This is very common in high energy processes.)

Quantum fields are REAL because certain phenomena like solitons, vortices, monopoles and quark confinement can only be understood properly in the full field context. Quantum field theory cannot describe these phenomena in terms of Feynman diagrams. Feynmann diagrams and scattering cross sections/lifetimes were once considered fundamental and fields were believed to be a tool to derive them. Physicists now understand (the competent ones) that Fields are more fundamental than the diagrams. The Fields are also real in the sense that the do much more than just represent particle states, field symmetries are fundamental symmetries of nature, e.g. the strong force has SU(3) symmetry, electroweak SU(2)xU(1) etc.

Steven Weinberg gives a very strong argument for the necessity of fields in his vol. 1 QFT book. It's very technical but a brief summary is... QM + relativity + cluster decomposition principal (which more or less says the results of distant experiments should be unrelated) --> fields