I am by no means an expert, I still am wearing my apc's and haven't given them a wash yet.
From what I have been told is to hand was them, fill up a bath tub and weigh the jeans down with some full 2 liter soft drink bottles.
As for the amount of vinegar to use I don't know. But I'd fill the tub, pour a generous amount of vinegar to the water and let soak for a few hours. Then give them a solid rinse with fresh water and air dry.
As for the stretching...