Turbo questions

This is probably a silly question, but I was wondering how different sized turbos affect fuel economy.
Can anyone give me a brief synopsis?

They dont - directly. A larger turbo can produce more boost safely, and if you have fuelling and a chiptune which demands more boost than the stock turbo, then you'll get more power. If you don't use the power though, your mileage will stay about the same.

They're all related. Being ABLE to push more air into the motor doesn't equate to more or less power or economy, its what you do with the air that matters.