You don’t want to compromise taste, and you want your cream cheese frosting to have the best taste ever, just keep the ratio 2:1 cream cheese to butter.
Now, about the cinnamon amount. It depends on how cinnamony you would like your Cinnamon Cream Cheese Frosting to be.
I like to use Ceylon Cinnamon! It's also known as real cinnamon. Ceylon cinnamon tastes better too.