I think a MBA would be perfect for your needs.
A 15" MBP would be too heavy and pricey for college and I guess you wouldn't need its performance either. I think the 13" MBP is a little awkward right now and has nothing over the MBA unless you need a lot of storage or more than 4GB or RAM.
The MBA will offer a better screen resolution, faster boot/loading times, more convenient USB placement and would be lighter to carry around.
Rumors are that the MBP could get updated this summer though, but chances are that the 13" MBP could disappear. Time will tell what will happen, but if you're in the market right now I say definitely grab a MBA, it's a fantastic computer that seems perfect for you.
As for Office, if you don't currently own it you can choose to buy and download it legally from Microsoft's website. You can also download the full version for free
here and it will expire after 30 days. After that, simply enter the serial number from a boxed version and it will activate permanently.
If you already have it on disc, you can use another computer's disc drive and wirelessly share the disc using Remote Disc (instructions
here).
PS: I constantly use my MBA to edit 18MP photos with Photoshop CS5 and it's plenty fast. You should be fine with Aperture too.