rat is about right.
Rule of thumb is 10% by weight.
For 1 litre of water add 100g (by weight) milk powder. You will not have 1100 ml of milk, as the powder dissolves and absorbs water, it is still about 1 litre, barely little more.
For 8 ounces add 3/4 ounce (by weight) of milk powder.
This is for whole milk powder. For high temperature skim milk powder 1-3%.
For breads and cinnamon rolls you do nut have to dissolve the milk powder. Just blend it with the flour and it will hydrate fine in the dough mixing process.
The milk powder is the functional portion of the milk that not only lends richness to the product, but also emulsifies the fats with your flour and water, producing the nice even grain structrue that helps provide the tender and moist mouthfeel. The lactose also helps to promte a more golden and even mallard browning of the crust during baking.