I use 1 oz of fresh lemon zest in my lemon wheat which is pretty good. Not too strong but there is a good presence. I also use Grains of paradise to compliment and balance the zest.
I would say 0.25-.5 oz of each if you are using zest. Maybe go on the lower end since you aren't using any other spices such as coriander or GoP.
Just my thoughts.