Nice photos of Bülow, the second postcard I have seen before, the first photo in the uniform of a Sergeant or perhaps Fähnrich, I never saw before. Are these in your collection?
With the Austrian photos, I assume the first card is of two Gebirgsjäger - or possibly Kaiserjäger, there is an Edelweiß on the green collar patches (grüne Egalisierung), I think this is the new pattern of uniform with puttees and tunic with turndown collar rather than the standing collar at the beginning of the war. Field grey was introduced to replace the previous "Hechtgrau".