Am I grabbing at too much here?
Probably. Some thoughts...
3 nights in Munich probably won't allow you to cover Munich, O'fest, Garmisch, AND Dachau (if that's what your plan is, not sure.)
If you are heading to the Swiss Alps anyway, I think Garmisch is probably an unnecessary detour.
The Alsace is near the Black Forest (as travel4fun points out) and combines well with a train trip into Bern and the Bernese Oberland (and perhaps onward to Gimmelwald, or Lauterbrunnen, or Mürren) via Basel.
There is another very big German "Oktoberfest" known as the Cannstatter Volksfest (Sept. 22 - Oct. 8) which takes place in Stuttgart and has been an annual event for the last 175 years or so. Stuttgart and the Alsatian city of Strasbourg are only 80-90 minutes apart by train.
So I'm thinking Munich etc., besides being crazy expensive during Oktoberfest, is looking like a destination too far and that your Germany-time would be better spent closer to your France and Switzerland destinations. Basel would be a sort of central point for your 3-country visit. There's actually a monument there that marks the spot where the 3 countries meet called the Dreiländereck.
So maybe your revised, more compact itinerary would break down roughly as follows...
Fly into Stuttgart (or maybe Frankfurt, then take the direct train - just 70 minutes - from FRA airport to Stuttgart.)
1.) 5 days for Germany: Stuttgart for the Volksfest + nearby places + the Black Forest towns
Good options accessible by train include... Esslingen - Tübingen - Gengenbach - Gutach Schwarzwaldbahn - Freiburg
2.) 4 days for France: Strasbourg? Colmar? Just 30 minutes on the train between these two.
3.) 5 days for Switzerland (Bernese Oberland... Lauterbrunnen can be reached by train and is a lovely base town for Mürren, the Schilthorn, Gimmelwald, Grindelwald, the Jungfrau...) Look into Basel as well - it might be a place that interests you. You'll probably need to overnight in Zurich prior to your flight out; it's a nice city to visit on foot and shouldn't require more than half a day or so.
Fly out of Zurich (about 2.5 hours by train from Zurich)
There is a concentration camp memorial site in the Alsace roughly in between Strasbourg and Colmar if you really feel visiting one of these is appropriate/imperative: