Todd, I have not taken the train from Munich to Milan, but have from Munich to Venice and what an experience. Now if I had taken the plane, I would not have written about it. Shirley and I had no experience with trains, being from the south in the US, trains are not used (rarely). I had to teach myself to use the train system first in France, then Germany. I was a bit apprehensive at first on taking the train, but my fears were soon over after taking a few rides. Our trip from Munich to Venice was a Kodak moment around every bend, we stayed glued to the windows. We sat in a open 2nd class coach room or cubicle. meet a couple from the US and a elder lady from Italy, I used my 3 words of Italian I knew and discovered she was going home to see family. That was 8 years ago and I still recall every moment like it was yesterday. By research you will figure out if you need to reserve a certain route on the train, most times you can purchase the ticket at the station thru a machine, Don't be intimidated by it, if you can read, you can figure it out. YouTube and this site is your best friend.
The Hauptbahnhof in München,(two words you need to know) is so great!!, Busy, loud, full of travelers, local and tourist heading all over Europe, Be a tourist, take lots of pictures., Have fun