I was able to create this functionality (a popup message about the shop being closed) by putting the shop in pause mode and adding the "Product Warnings on Checkout" app, for $10 a month. Facepalm. 

I totally agree there needs to be a simple vacation mode with the click of a button. Every other selling platform I use offers this (Amazon, Etsy, Faire, Woocommerce, etc.) I'm not accepting orders for two weeks while I'm closed—customers will be ang...