Great choice with the 320d, BMWCar magazine did reviews on the 320d coupe this month and last month, sounds like it's a great drive.
Think they said there was a claimed consumption of 55mpg combined compared to the E46 one which had 46mpg combined.
If the E46 320cd is anything to go by (a mate has a 2006 one and it's great), this should be a cracking car.
Long may you enjoy it.