Foundation milestone
Working definitions: naad, swara, saptak, that, jati, vadi/samvadi, laya terms
Intermediate milestone
That system & raga classification, time theory, biographies of great artists, Hindustani–Carnatic comparison
Advanced milestone
Shruti–grama–murchhana theory, the treatise line (Natyashastra → Sangeet Ratnakar → Bhatkhande), acoustics, aesthetics (rasa)