Not much time, thus I will only try to add here some things until I have more time tomorrow to add more:
1. Wilhelm the 2nd: Despite his quick-tempered character, his reputation is actually worse then it should be. In contrast, after speaking out Germanies support to A-H after the killing of the crownprince, which can be seen as a mistake, he was one of the few people who actually tried to prevent a war or to keep it at least local. He even thought after the Serbian answer to the Austrian ultimatum that there would be no war because it was seen by him as enough and a political victory.
Unfortunately important German diplomats who favoured a war had quite some influence (and Wilhelm II. actual influence in the events of the July are also overrated).
2. "Illusions of a fast war": I wouldn't call it illusions, especially not when it is your only chance of winning the war at all (Germany never had in his history the ability or the luck to be able to fight a long lasting war, especially not when you are "surrounded by enemies"). Also the initial German attack until the battle at the Marne actually proved the ability that such a war was possible, later the 2nd world war proved again that quick victories are in fact possible. Even during the Great War the eastern front for example was far more "fluid" and the collapse of the Italian army at the Isonzo proved the possibility of quick-successes too.
Even on the western front, the Germans fought far more maneuverable than their foes on a tactical to operational basis.
The lessons learned of the first world war from the German side actually found the basis for the successes of 1939 to 1941.
3. German - Austrian military cooperation: There were huge differences in Command and Control between the German army and the Austrian army. I'm not sure if a military cooperation was actually so easily possible.
To the questions: Was the war inevitable? Yes, pretty much. This can be especially seen also in the populace of the countries which cheered for the war pretty much everywhere. Something that never happened again to the same extent in every other war AFAIK.
Edited by Thonar3, 28 June 2015 - 1257 PM.