90% of the country has only one band director at a school. We are spoiled in Texas because it's all we know. Before moving to Texas, I taught out of state and had over 200 students. 3 large concert ensembles, two jazz ensembles, jazz combo, large percussion studio, color guard class (I brought someone in for this twice a week), marching band in the fall, solos & ensembles.... I was the only director and we were successful. You're lucky to even have a long term sub. Just count on them for supervision of students where needed.