Hi Michael. I took a similar path during my senior year a little over 20 years ago and my personal experience was a good one. One thing that really helped my situation was that the college classes I took also went toward the high school credits I needed, so I wasn't doing 'double' work. This was a BIG factor in my decision to pursue early college classes. Sure the courses were tough but I had good study habits, so it didn't take me significantly longer to study for those classes. That left me with enough time to maintain all of my school activities and social life. For me, the benefit was going into my Freshman year with 9-12 credit hours (I can't remember the exact number). That helped me graduate from college a semester early and cut down on my student loan debt.
There is no right or wrong answer to your question. I believe it comes down to your individual circumstances. Weigh all the pros and cons. Do you get dual credit for the classes? How many hours a week do you need for activities and being social vs. how many extra hours do you need for classes/study? In addition to increasing your chances of acceptance at MIT, what are the other benefits to you long term? If you don't do it and/or get into MIT, what would you do? Would you be happy with that? If you get into the program and it's too much, do you have an option change your mind? Be honest with yourself as you answer and trust your instincts - they know you best!
No matter what you do, it sounds like you're heading for great things! All the very best.