Instead of developing something from scratch is there any existing commerce kind of add-on that could speed up integrating FoxyCart and members? There are no products, codes, categories, or anything else in my EE yet so how that gets put into EE can be completely subjective at this point, too. I haven't really touched anything asides from the Simple Commerce Module in EE 1.6.x.
For those of you not familiar with FoxyCart it basically does not assume anything about your e-commerce, it doesn't hold products, but it does create customers invisibly on its end (you can use their API/DataFeed to communicate from your end and/or to receive updates on their end). It keeps track of transactions and can make recurring subscriptions regardless of your merchant gateway. You provide FoxyCart with all the information based on your cart/checkout, such as products, discounts, coupons, categories, you make it all up (can be done securely so the data can be determined to not have been tinkered with) and FoxyCart will present your user with a cart, checkout, etc. It's completely open-ended so you can make your own user experience as you please.