We are planning on visiting some parts of Germany and Austria in late August/early Sept. and could use some help in refining our plans:
We will be arriving in Munich. We have a good friend in Fussen so part of the plan is to spend one full week in Fussen and take day trips to some nearby sites recommended by our friend, That would leave us with about 10-12 days to visit places that are outside the range of day trips. Our current thoughts are to visit Salzberg and Vienna and may be add Prague to the list.
We plan to rent a car in Fussen and one of our questions is: should we travel to Salzberg and Vienna by car or should take a train? If we take the car, is traffic and parking in Vienna ,Salzberg and Prague a problem and pricey?
I normally stay at SPG hotels but find that these hotels in Vienna are upwards of 300 euros per night (ouch). Any recommendations for clean cheaper hotels in early September?
If we had 10-12 days what would be a good distribution of the days between the three cities? We are NOT museam buffs but of course we would spend SOME time visiting them but prefer nice scenic places.

If late August/early Sept. is a BUSY time to travel, our other option is late October/early November. What kind of weather should once expect in early November?
Thanks in advance for your help.