If you plan to drive by car, Garmisch and Insbruck would be well worth a visit IMO. But it is quite a detour and you would need the austrian toll sticker (you can get it at most gas stations in Bavaria, a week sticker is 8 €).

A more direct route could be Prien at the Chiemsee lake with a short boat trip over to the Herreninsel and to King Ludwigs castle there. Then on to Berchtesgaden and from there the direct scenic local route over to Salzburg. No need for the toll sticker on this route if you return your car in Salzburg.

As an alternative to having a car all your routings could also be done by train. Good and frequent offerings - plan and book with www.bahn.de and print an online ticket. If you only use local trains consider the Bayernticket or Schönes Wochenende ticket.