I'm actually pretty thankful for the $5 off $30. Has me considering stuff like Ys VIII and Div OS2.
The $5 off is one-time and for not multiple checkouts, correct?
Terms say that it's valid on your first qualifying purchase, so it should be one-time use only.
Also, it's worth mentioning that the next Humble Choice goes live next Friday. Might be a good idea to wait and see what's in that since you'll still have six days left in the Summer Sale.