You'd be fine so long as you do like you're planning: change the bedding frequently and rats or soft furs. Mice are NASTY for smelling, especially their urine! One thing about Norway rats is that they grow to size faster than what do soft furs but they can also grow too large in that your snake wouldn't be able to eat it. It isn't too much of an issue if you're wanting holdbacks/grow outs but just something to be aware of. I know soft furs take a good while to mature enough to be able to reproduce, which if you go in knowing that and plan accordingly...anyway.
You really won't save any money raising your own, unless you can sell off some of your "extras" and/or if you have enough snakes that it makes sense economically to raise your own. It is pretty cool to see them produce and know that you raised what you're feeding your animals and when (or if) you get into the genetics of coat type/coloration/pattern, etc. then it gets to be almost as much fun raising the rats as it is the snakes, lol! Here's a few options as far as ready-made racks if you don't have access to woodworking equipment or don't want to build your own:
http://boamaster.com/catalog/Rodent_...acks-18-1.html
The price for the economy rack is right about what it cost me to build mine of the same style only with a few more tubs. Food for thought, if nothing else. Good luck and hope that helps!