...so I picked them up and began folding and storing all 600 of them (120 shirts in each of 5 designs). Once I figured out a good system, I was able to process the shirts at a rate of about 100 an hour. As you might imagine, the process - folding, folding, folding, stacking, breaking down boxes, and back to folding again - was a bit tedious, but at the same time, manual labor can be therapeutic in small doses.
What am I doing with all these shirts? I've stored them all in my garage, in 68-liter storage bins, which are each about the size of the freezer on a standard fridge. The garage was too narrow to store a car in, so the space was available. Here's a shot that shows the bins as well as my more typical garage gear: