I am currently applying for grad school and worried as well about how the work load will be. I did manage to get through a 4 year university already. I double majored, minored, and played a intercollegiate sport. One semester I did overload myself and took 8 classes during my sport's season. I found it took a lot of planning to find time to do everything. I also made sure I was super aware of how I was doing mood wise and would rearrange my plans if necessary. Some periods I would blow off papers completely and others I would bust out a bunch of assignments in a row. My last week of my senior year my friends actually doubted I would get all of my work done but I finished with 2 days to spare. Some grad programs allow you to spread out classes, a couple of my friends are currently doing this. You just need to research what colleges have what you want and see how they allow you to schedule classes.