I just moved my store from Modx with Foxycart to WordPress with the foxy shop plugin. It's now so much easier to manage.
With Foxycart you don't need an SSL as the transaction/payment takes place outside of your domain.
There isn't really a check list needed with Foxycart, but make sure that you get cart validation setup. This prevents people from manipulating the price before it's passed to the cart.
What CMS will you be using?