Add on a little bit at a time to see what you can handle. My list of priorities are, in order of importance:
1. Grades
2. Self care
3. Service
4. Shadowing
5. Research
I like the term "self care" rather than social life. Self care implies that you are looking after yourself first, which may include being social. You need to take care of yourself no matter how you fill your time. I highly suggest that you resist the temptation to cut the things out that you "don't need" like being social, having fun, etc. You do need them, which is why on my list I take care of my grades and self care over anything else. Come up with your own mental list and see what is important to you. Add numbers to your list over time, and assess how your life is a few weeks after adding an item up on there.