Thanks for your questions guys.
Red Hot Toys - I can't be 100% sure the logic will work in relation to line items but this does seem like the most logical approach so I assume we would go in that direction. I understand that you want to have as much control as possible but from a product stand point there is a fine line between giving too much control and making the product too complex or filled with options which are very rarely used. We are always working on improving this, so thank you for your feedback. One thing I did want to mention to you is that we are currently working on a really powerful new feature we are calling Burst Emails which will allow you to manually send requests for site reviews (and in a future version product reviews) from customers. This will solve your issue of not being able to send mail after purchase emails because of your inventory cycle.
GMCS - I am not sure of how the spam law would work in this case. It's something I will check. I can tell you though that we are sending over 100,000 of these mail after purchase emails a month to customers of our customers in dozens of countries and we have never had an issue of a customer being sued because of our emails. If your customers that didn't opt into receiving marketing emails really are unhappy with getting these emails then they can unsubscribe. I can tell you that almost no one unsubscribes from our mail after purchase emails.