Sorry, busy day at the office. I pretty much accosted Tim Brown all day...
Anyhow, get a Toshiba Chromebook and no, do not get a USB hard drive. If anything, get an SD Card and stick in the SD Slot. It will lay flush in the side of the Chromebook and you won't even notice it. You can get a 64 GB class 10 for the same money Sidehatch wants you to waste, which will give you 4 times more physical storage than the Chromebook allows, and combine that with 100GB of Cloud Storage Google is going to give you, you'll have nearly 200GBs of storage without having to carry around a stupid, bulky useless drive.
I've had the original Toshiba Chromebook for 2+ years now and don't have a single Windows Machine in my arsenal. The ONLY thing I need to use a different machine for is Lightroom....and for that I just Remote Desktop into a Windows machine or borrow the Mrs Macbook Air, which is an absolute waste of money.