Since Austria as of right now only has 1 small stamp series with the Vienna 4, I think one with Alpine plants would be nice, also because I think the connection of Austria with its mountains is no way yet reflected in the available stamps (theoretically this series would equally apply to countires like Switzerland, Italy or Germany).

These would be my suggestions for a 4 stamp series:

A quite common and beautiful flower that you find a lot in the mountains and that is also even used for the production of liquor and alcohol.

The only tree that still grows above certain altitudes though more in bush form. Famously used for the production of essential oils.

Commonly growing in the mountains, looking quite nice both when blossoming in light pink color and when the berries are ripe and deep red. Being used to product jam that is a big part of Austrian cuisine.

Common flower which pink blossoms in late spring makes the mountains really beautiful.