What I would ask myself
Why don't you use a shopping-card system?
An open source shop-system software is too much hassle to set-up and maintain, it is also permanently under hacking attempts (I have been burned before).
Now my bare bones order system is connected to a Google spreadsheet that updates itself automatically and forwards directly to PayPal.
Typically, a couple of features are missing, like a shopping card which adds products to a list. With this system, only one item can be ordered.
But if you want to order more, I will issue an invoice with the best prices and shipping solution for you! Please contact me here.