I think you're making a wise choice.
As for breeding rats, most euthanize using a CO2 chamber like you mentioned. It seems the most humane way to go. From there you can freeze them or offer what's known as "pre-killed" which poses no risk for the snake.
As for purchasing F/T prey Petco and PetSmart have poor quality prey at ridiculous prices. There are online suppliers who have ethically run facilities and produce quality prey for a whole heck of a lot cheaper than the big box stores.
I personally use perfectprey.com or bigcheeserodents.com but there are others. You can also find prey at expos for comparable prices to the companies I mentioned without shipping costs.
And yeah...morohmarket is fantastic and evil at the same time, hahahhahaha. I want this one...and this one...and this one..etc......hahahahahahahaha.