You can't really skip anything. Concepts and techniques recur, over and over again. Half of dealing with the "advanced" stuff is just taking its leading order t

You can't really skip anything. Concepts and techniques recur, over and over again. Half of dealing with the "advanced" stuff is just taking its leading order term and pretending it's classical. Quantum electrodynamics is fun for explaining atomic physics and below, but for everything bigger than a molecule it's useless and classical E&M rules the day. So... yeah, you've got to start at the beginning. Or at least, know what you're passing by.