That's a major limitation.
U maybe able to use an external drive but then u can't sync while on the road until u take the external w you.
seconded. that's pretty small for a primary drive. unless of course you have regular access to a storage device like a drive or even your phone.
usb3 is pretty darn fast. functionally you can move quite a bit of data relatively quickly...
then the cloud has gotten better and better - i store all of my photos on dropbox. i take a picture with my phone and it gets uploaded to DB and periodically i delete pics off my phone.
i agree with others - most of us have huge music collections, but they do tend to cap out around (whatever i say here people will argue with so i'm jut going to assume you know your own music needs)
the big decision to me between the small and medium ssd ont he 13" mba is whether or not you're going to run a virtual machine. If the answer to that is yes, then definitely you're going to want the 256 imo.