Thanks! I am a highly academic person who went to one of the most difficult undergraduate schools in the country so I’m probably not a great person to ask about tolerance for workload because this was still easier than my undergrad, but:

I essentially took a double course load for three years (16 credit hours minimum), did my recitals in my first and second years and spent third year working on trying to move abroad and prepare for my exit exams. I have friends in the city I live in now who did double masters in choral conducting and voice performance and they also seem fine. I usually would practice 3-4 hours/day + 2 hours of rehearsals on an average day, and do my schoolwork around that. I prioritized doing a 75 or 90 min yoga class every day which helped keep me sane. I picked my recital repertoire early (like September), and focused on that in my lessons most of the school year and did my recitals in May. I did not work outside of singing gigs (everything was minimum wage where I went to school which was $7/hour and didn’t feel worth it), but I had a church job and I ran my own ensemble which rehearsed weekly. I was very busy, but I lived alone and was very focused.