Thank you so much for your help.
I am very diligent with data usage- I have only 2.3 GB of music (a lot of which I can delete) and no videos. I almost exclusively use the internet for my media needs (Pandora/Netflix/Hulu Plus). On my current 2010 Dell Studio I have only used 72.8 GB of space, which lasted all of my undergrad. It has a few small data sets and probably 100-150 journal articles saved, along with all of my work. Obviously, I will be reading, writing, and computing data sets much more often in grad school, but I feel pretty comfortable with a 256GB SSD given my low usage of storage. I can grab a decent-size USB if my needs dictate it, which is of no concern to me either.
I plan on investing in AppleCare for peace of mind, too. Also, for what it's worth, I have an iPad with iBooks to store some reading materials on.