we will be starting our trip in the Netherlands, how many days will we need there? about 4? then going to salsburg, austria next? or from Netherlands to munich, germany next then salsburg? then on to paris, france. plan about a three week trip in all and will go by trains.
A few pointers:
Get yourself a map of Europe. On that map, mark off where you want to go. Think of going in one direction without backtracking and possibly even a circular route.
At the top of this webpage you'll see a link "Plan your Trip." Utilize all the information there. Even better, get yourself a copy of "Europe Through the Back Door" by Rick Steves. It will answer just about every general question you'll have. (Both have lots of information on how to plan a trip.)
In Munich, purchase a Bayern ticket to Salzburg.
What time of year are you going?
I think that 4 days in Amsterdam is too much, unless you will be doing day trips from there.
Frank II has a very good suggestion to get a map of Europe and plan with that. I wish I had done that before my first trip. Try not to back track.
For the areas you referred to I like Steve's suggestion.