8-10 nights for Salzburg/Berchtesgaden is a very long time. I didn't take the SOM tour, but it took me only about an afternoon to explore Salzburg. The Altstadt is very small, and compared to many other Bavarian/Austrian towns, in my opinion, kind of monochromatic. Berchtesgaden is very close by. You could conceivably just base yourself in one of the two places. With that much time devoted to this one corner, feel free to break out of the Rick Steves-approved universe. Consider daytrips to Passau, Burghausen (one of the largest castle complexes in Europe), Landshut, Chiemsee, etc. Check out some of these other towns and you might see why I wasn't blown away by Salzburg, nice as it is.
No need to go all the way to the Black Forest. It has great name recognition, but it's just one of the 50 or so forested mountain ranges that criss-cross southern and central Germany. And it's peaks pale in comparison to the Alps, of which you'll already see quite a bit. If you want to see a similar mountain range, just check out the Bavarian Forest, between Landshut and Passau.
Baden-Baden is another skipable destination. Once again, it's only one of about 100 or so officially designated spa towns in Germany, and many of us find it far from the most interesting. If you want this kind of ambiance and you want to experience a spa, look into Bad Tölz, Bad Aibling, or Bad Reichenhall, all of which are much closer to your other destinations. Or if you just want the ultimate spa experience, go to Therme Erding, which is very close to the Munich airport.
Parking is ample in all the destinations you mentioned.