Thanks so much for your questions! My answers are below:
1) I definitely did not feel like my choice to pursue medicine limited the classes I took at college! I attended a liberal arts college. Although it sometimes took a little bit of juggling, I was able to take classes across a wide range of subjects (history, English, film studies...you name it!) while also completing my pre-medical requirements. I will say that for the most part, many of my pre-medical classmates did pursue majors in the sciences (biology, engineering, chemistry), but there are definitely exceptions. One of my closest friends was an English major at Stanford and went on to attend medical school at Harvard!
2) I think that it is helpful to know you want to be in medicine early on in college for two reasons: completing your requirements and getting good extracurricular experiences. However, you can certainly make it work if you are not 100% sure! My suggestion would be to take 1-2 science classes your freshman year so that if you decide you DO want to pursue a career in medicine, you can complete your pre-medical requirements without having to do a post-bac program. Additionally, it is becoming increasingly common to take time off between college and medical school (I took 3 years off!) so you can certainly have time to get some good volunteering/research experience under your belt.