I suggest a change for the strategy. Honestly, you dont need to attack montenegro right away, and the german units may be used well elsewhere in those beginning turns, serbia wont be able to go on a offensive against austrians for some time.
Austrians should focus on attacking Belgade and Valjevo, you attack Cetinje similarly (and similar effect) with German units in 1915 when Albania joins the war and kill two birds with one stone. This offers several advantages:
1-immediately, you get additional route of attack through albania, outflanking serbia even more and stretching them thinner
2-austria can rest for sometime after initial objectives and focus on Russia (ties in better with east first strateggies and can save them some money)
3-plunder and income will mater more in long run, along with ability to plan spending better as mentioned above if you capture albania also (its not much but always something, its important to divide the spoils in the Balkans between the 3 big players for most optimal performance)
4-Additional route of attacking eventually into Greece later, this can be a disadvantage if Entente invests in Greece, but i feel like its easier for CP to muster units here than Entente in the end.
5-Albania gives you an additional harbour, and when Greece joins you can take Corfu very early and it gives you a lot of uses in your struggle in mediterranean.
Of course, Cetinje may be defended much harder, but with if you time it right, coordinate, Serbs have to give in either in Montenegro or in Serbia proper.