Here is some idea, since I have to do it almost every week at home.
Individual size, would require four to eight tea bags, maybe more or less, when experimenting, for a single cup. The soak for those are two to three hours I think, it can be more or less, just taste it.
This is for making bigger quantities.
I just boil a gallon of water, more or less, based on the container, put in the tea ball. Tea bags, use usually need a clip of 20 or 30 tea bags to be equivalent or close to it.Then soak for five hours minimally, that is what I found out, more would be required if you added more water. It would be less with less tea, when used. More hours or time should be added or lowered, based on how good or bad it is, as well.
As for milk, I prefer it with whole milk, for you can taste the milk and tea better, without it becoming over-sweet, which I tasted a lot when I was in Taiwan. You can use condense milk, evaporated milk, whole, and low fat. For low fat, you have to get the ratio right, for it would taste watery. When making it, due a ratio usually of one third to two third, based on the cup. The ratio will change based on how strong the tea is, and what you use. Whether is whole, low, evaporated, and condensed.