DH and I did it last year, I think we booked that previous Oct-November. I think others booked in like January/Feb. You are going to have a great time. We really enjoyed doing the adults only departure. I found we got a bit more info at the Neuchuwestein than you might on the ones with kids.
If you can try to stay an extra day on either end, it's nice to have a bit extra time in Munich especially since you are there during Oktoberfest. We took the extra day to go there.
I can't say enough good things about the trip.