Since you spelled Salzburg, Salzbury, twice, I'm assuming it's not a typo. You really need to do a little more research, particularly on transportation.
Even renting a car in Freilassing (I don't think there is a car rental at the Freilassing Bhf, but there is one at Salzburger Platz, which is a stop on the bus coming out from downtown Salzburg), I think using a car would be substantially more expensive than using public transportation.
There is a bus going from Salzburg Hbf to Bad Ischl with a stop in St. Gilgen, then take the train and boat from Bad Ischl right into downtown Hallstatt. Or, you can go further by bus from Bad Ischl to Lahn (1 km south of Halstatt, which is where you would have to park a car if you drive).
You can take trains from Hallstatt to Rothenburg. With a few stops in Attnang Puchheim, Linz, Nürnberg, and Ansbach.
The last day take the train via Würzburg to Frankfurt.
Use the Bahn website to find connections. It will also show fares in Germany. The bus fare to Bad Ischl via St. Gilgen will be nominal; you can buy the ticket on the bus.