A very changed final itinerary
 

We started with a plan to cover Vienna, Salzburg, Rome, Tuscany and a bit of Southern France in 15 days. We dropped France first.....and now, we are driving around Austria and dropping the Italy bit for another trip.

So this is the final plan:

Vienna - 3 days
Prague - 3 days
Cesky Krumlov - 1 day
Salzburg and Lake District - 3-4 days


That takes us to 10 or 11 days and we will have 3-4 days to get back to Vienna. We were thinking of driving further to Black Forest or down to the Dolomites. For both these, we want a leisurely drive than wanting to see anything specific. I am told both these can be very scenic.

My hotels till Salzburg are booked - so cannot increase a day or two in any of the first 3 place. Any suggestions?

Forgot to add - we will be renting a car at the time of leaving Vienna and dropping it off back in Vienna. Ideally, wanted to pick it up after the Prague bit, but one way rental drops are just too expensive....

Good for you---better plan.

Add Hallstatt and the Wachau valley at the end.

Since you are in the Salzburg area you might consider a day in Munich if you haven't been there before.

You should do you return leg from Salzburg to Vienna via Carinthia. You will get to see at last some real mountains.
Otherwise you just get the few peaks around Salzburg, which are just the overture to the real thing.
If you go in summer, the Grossglocker Alpine road is a great way to go across the Alps.
You can include a short glimpse of the Dolomites also that way, but it may take a bite out of you plan to have a very leisurely drive.

We were inclined to do the Grossglocker Alpine road - and we will probably add a little detour to get a glimpse of the dolomites. That will probably be a full day trip.

That leaves 3 days - does it make sense to drive down to the Black Forest (Freiburg from Innsbruck looks to be a 4:30 hour drive)....we will probably want to see some villages, maybe buy a cuckoo clock and stay in the countryside 2 nights. Doable?

No.
That is nuts if you have to get back to Vienna. You will spend a huge amount of your time on the freeways. The Black Forest is a pretty huge area. And 4.5 hrs drive time from Innsbruck will be closer to 5.5 hrs or more in reality.
And also would only few people consider the drive from Salzburg to the Dolomites via the Grossglockner road AND BACK a daytrip.

I second the Hallstatt area. It is beautiful. Definitely plan to return and spend more time there.

Why do you have to get back to Vienna? fly on a multi city or open jaw ticket and fly home from Munich.

To save the cross border drop fee you could drop the car in Salzburg and train to Munich.

Aisleseat, should have. The flight came first and the itinerary later :)

As I said, the itinerary kept on changing and I had to get the tickets done for the visa.....