For a driving trip, the Michelin Green Guide is essential. It has maps laying out the location of what is worth seeing and recommended routes (I always use the maps, but usually ignore their route in favor of my own which I put tegether from their basic waht to see map).
If you drive in from another country, you must buy a window sticker to drive in Austria (technically, only for the expressways, but you will need them).
Plan two itineraries, one for good (natural sights) weather, one for bad weather (cites, museums, quaint towns).
With that much time, you can do something very unique, visit the Klienewastertal, An Austrian mountain valley (tal) that is only accessible by a three day hike over the mountains from Austria or by road from Germany,
Visit lots of pastry shops and eat cake. Austrian cake is very different from US style cake, which we don't eat anymore.
Don't make advanced room reservations. The country is full of small family owned inns, most with restaurants-- real home cooking.. Standards are very high, so we never worry about whether or not the room etc will be OK. It always is. Don't know if they still do it, but all hotels were rated * to ***** by the government, ratings that mainly reflected the level of amenities. * is pretty basic, but cheap. We usually stayed at *** which were about equal to a Best Western in the USA.
The little places offer a chance for an experience. Some examples: 8 rooms, a bar & restaurant. After diner, went in the bar and joined the natives in singing folk songs until 2:00 am when the band went home. How to sing folk songs in Austria or Germany: the tune is easy to pick up. All the lyrics can be done as la La La elc
Off season at a ski resort. We were the only hotel customers. When we went down to the empty restaurant for diner, the proprietor invited us to join the family for their daughter's 16th birthday party & celebratory diner.
Off season at a ski resort. Noisy music at midnight. Called the desk & asked when it would stop. The desk said, "it's a wedding reception. Come on down and join the party and we did, (in our PJ's), being welcomed like long lost family members.
The morning after I met Soviet Premier Gorbachev late at night on a dark and foggy street, the hotel proprietor joined us (me and spouse, not me and Gorby) for breakfast and spent 45 minutes regaling us with anti-Russian Austrian jokes.
A small bar in small hotel in the middle of nowhere near the Iron Curtain. A guy comes up to me and says, "Excuse me, but are you a real American?"
I said, "Yes"
He says, "I'm a retired Soviet Intelligence Officer. My job was to eavesdrop on US Air Force communications and analyze them for military significance, but I never met a real American. May I touch you?"
Forget guide book recommended hotels. They are going to be geared toward America tourists and likely full of the same. Venture out into real Austria, and who knows what might happen?