I was planning on just taking physics courses next quarter (3, maybe 4 total) but I have an interest in taking a number theory course. Would it be too much to pile on with QM, Relativity, a physics-based math course, and part II of E&M? I know this question is impossible to answer because each individual person handles things differently. So let me rephrase the question: How rigorous is Number Theory? Am I potentially putting a gun to my head in attempting to take on these courses all at once? Any advice would be appreciated.