That's an interesting statistic on music majors and bio majors, do you have a link? Was there some theory as to why, or just that (as you say) major was irrelevant?
Edit: Side note, would you recommend taking the prerequisites closer to when you take your MCAT/apply to medical schools if in a non science major? Are there classes that will be good to have fresh in your mind for the MCAT? Or is all that covered in average MCAT prep?
I do not have the link. You can find it though or someone else might supply it.
The reason why is debated a decent bit on here. My belief is that people who major in something like music and are pursuing medicine 1) understand the system well and 2) are passionate people. By 1) I mean that if you go into music and are pursuing medicine you are privy to the fact that you can get in with any major. If you are knowledgeable about that information you are probably also informed on applying early, PS format, EC tips and strategies, MCAT study plans, etc. A lot of people majoring in bio know all this too, but you also have a large group of uninformed premeds who think biology is the only way to go to medical school. These people are probably also ignorant of all of those important application factors and will not fare as well.
2) Someone who majored in music most likely really has a passion for it, and could thus often have a deep passion for their ECs as well. This builds a strong applicant.
But for you, personally, major in whatever you desire.
As for "Should you take the MCAT right after your prereqs if you don't go bio/chem" the answer is it depends. One should take the MCAT when they have had all the prereqs and have had ample time to study intensively. If your schedule/life plans/summer engagements allow that to happen so that you take the MCAT right after your prereqs then that is great. If however you finish your prereqs spring sophomore year and take the MCAT May junior year, you won't really be at a loss. The info will come back quickly in the first couple weeks of studying and you will have lost very little in that year.
For me personally, I am crunching my prereqs together and taking the MCAT right after. Gen chem freshman year, bio 1 last summer, ochem 1 phys 1 this semester, ochem 2 phys 2 bio 2 next semester, genetics and/or biochem next summer, MCAT in August. I just want to do it that way so I can be generally done with science for the last two years of my schooling and not have to worry about sGPA or MCAT. You don't have to do it that way though.
Spend some time on these boards. All this info will osmose (that can't be a real word) into your system.