Here is how I would do it.
Fly to Amsterdam, 3 nights
Fly to Venice. 3 nights
Night train from Venice to Salzburg. There are 2 night trains available. The one from Venice proper drops you in Salzburg at 4 am, so do not take that one. The other one you have to get from Padua and gets to Salzburg about 6:30 am. In fact, spending a day in Padua is well worth it. Go in the morning and store luggage at the train station. Or skip the night train and take a day train and see the Alps. Takes about 6 1/2 hours on a direct train to Munich.
Munich, 4 nights. You can take a day trip to Salzburg using a Bayern Ticket.
Fly home from Munich.
There it is. Add or subtract a night here or there as you get further into planning. Most people here don't use tours, excepting of course, those of our host, Rick Steves. You buy your own airline tickets on line. Long distance train tickets on line, hotels on line, other things locally. That is the raison d'etre for the Travel Forum, sharing knowledge and ideas.