Hi Lisa,
Welcome to the forum, sounds like you've worked out most of the 'guys' around here.
Good choice on the 320d E90. The spec sounds great and its good you got the USB option. I've got the convert in the 320D and I get 52MPG with some speed on top so early 50's should be achievable.
I take it that this is a company car and so mods are out of the question? If not however, I would recommend the sunglasses mod which converts the cig bin into a sunglasses holder and if you ever want a little more punch, get a remap.
I'm sure you'll love it!
Pete (For the record also under 30!!!
)