I think that a complete Ottoman victory over the Balkan powers is impracticable, though possible with a POD going back a few years. I don't see the European powers sanctioning more than a few minor territorial gains for the Ottomans, as historically they were loath to see the Ottomans expand their borders at the expense of Christian powers. Case in point, the Ottomans had won the 1897 war with Greece decisively, yet Greece eventually received Crete anyway thanks to great power intervention.
Unfortunately, I don't know enough about the politics of Serbia to make a judgement about a possible lead-on to WW1. As far as I am aware, part of what made Austria-Hungary so jumpy about Serbia in the first place were the large territorial acquisitions she made during the First Balkan War, so perhaps if something similar to the assassination of Franz Ferdinand happened in this timeline, the Austrians would be less willing to go to war, or at least would be less aggressive.
As for the Ottoman Empire joining the Central Powers, I'm not quite sure. One of the reasons why the "Three Pashas" were able to seize power in the first place was the discrediting of the previous government due to the severe losses in the Balkan wars. The Three Pashas were more pro-Germany than most of the ruling strata of the Ottoman Empire (Enver Pasha had to go behind the back of most of the cabinet to sign a defensive pact with the Germans in the run up to World War One). Although the Ottomans and Germans had close ties anyway, I see it as being rather difficult to get the Ottomans to risk joining the Central Powers in the event of a ATL World War One if they don't have the Three Pashas pushing them into it.