yes, the yogurt makers are a good investement, it will pay for itself in no time at all. thats the best way to address the "how much heat" question.
as far as how much milk and how much bio k, well you need to experiment. do different amounts of each, but be sure to keep careful notes and label each jar so you know what works best.
i like this style of yogurt maker because you can do more than one batch at a time.