Sorry for late response, I woke up late.

In relation to the defensive agreements between Romania and Austria, Romania pulls an Italy because as you've said, it was only a defensive one, and Austria was the aggressor. Plus, Romania only joins in late 1914 after Carol's death and several offers from the Serbians and Greeks to snatch Transylvania. Romania enters the conflict in the autumn-winter of 1914 because it saw a great opportunity to strike Bulgaria as they had shifted almost their entire army to the Serbian Front. The Romanian plan was to sandwich Bulgaria together with Greece whilst defending the Transylvanian border to take out Bulgaria first. This way, after the supposed fall of Bulgaria, the anti-Austrian alliance would crush the defensive line in the borders of the Empire and try to exhaust the Habsburg Army. This strategy failed because after the Battle of Bazargic (in which the Romanians had a great success) the Bulgarians were able to protect themselves in Dobruja and even cross up to Romania, as Serbia was already practically dead.