Driving to Flachau: the A10 vignette and where the Tauern toll begins
Does driving to Flachau need the Tauern tunnel toll as well as the vignette?
No. ASFINAG's own product page puts the A10 Tauern and Katschberg section toll between the Flachau and Rennweg junctions, and Flachau's Exit 66 is the Flachau junction, so a car that leaves there stops short of the charged stretch. The vignette you do need: coming through Salzburg it becomes obligatory at the Salzburg-Nord junction.
Exit 66 sits before the toll boundary
ASFINAG's product page for the A10 states that the Tauern and Katschberg tunnel toll applies between the Flachau and the Rennweg junctions. Exit 66 is that Flachau junction, so the moment you leave the motorway is the moment before the charge would have started.
Direction of travel decides this. A day trip on over the Tauern Tunnel and the Katschberg Tunnel towards Carinthia enters the charged stretch and is billed separately at the route, on top of the vignette you already hold. Turn off at 66 both ways and the section toll never comes into it.
The vignette starts at Salzburg-Nord
Flachau's own travel page sends drivers from Germany and the Netherlands by way of Munich and Salzburg, then south on the A10 Tauern Motorway to Flachau Exit 66.
The A1 Westautobahn is outside the vignette requirement between the Walserberg border and the Salzburg-Nord junction. From Salzburg-Nord on you need one without a break, through the Salzburg junctions, onto the A10 and down to Exit 66.
Set the start date of a 10-day vignette to the day of the outward drive and the return is covered too, as long as both fall inside ten consecutive calendar days counting the first. Check the current Austrian vignette prices against the length of your stay before choosing.
There is no useful vignette-free way in
We could not find an official toll-free approach to Flachau from the north. The only alternative on the map leaves the A10 earlier at the Ennstal exit for the B99 and B320 through Radstadt and Altenmarkt, and that is a long westward detour that still uses the A1 and A10 up to the point where it turns off.
So the honest answer is to take the published route and hold a vignette for it.
The short-stay zone is 22 spaces
Flachau's official Kurzparkzone is 22 spaces on Am Hammerrain, west of the parish church, with a maximum stay of 180 minutes fixed by municipal ordinance. It is a place to collect a lift pass, not to leave a car for the day.
A ski week's worth of parking is not something the village centre offers, so the car ends up wherever your accommodation puts its guests, and that is worth settling before you arrive.