Perusing the 4-page list of street closings during River Festival (May 9-17), it appears as though you would have the most difficulty getting to the shop from the northeast.
These streets will be clear the entire time:
Douglas (west of Sycamore only)
Sycamore (south of Douglas only)
Parking behind the shop will be roped off for customers. That is, if you're a customer, you can cross the rope and park. We'll do our best to keep it clear for you. Otherwise, street parking will be pretty scarce, so look for parking on the side streets south of Douglas (Oak, Osage, Texas).