I too recently had to deal with this dilemma, to breed feeders or to not breed feeders. Being that my collection is constantly growing and the fact that I'm breeding my snakes I felt it would be wise and cost affective to breed my own feeders. Not only does it save money after the initial startup cost I also know exactly what my snakes are eating and it's only the best. Currently I am working with one rack of 8 mortar tubs housing 1.2 in each tub and will be adding an additional female (that I produced no outsiders) to each tub by the end of the week. At any given time I'm housing anywhere from 100 to 200 rats counting the babies. I do all of this inside my home in the same room as my snakes with no issue of odor and it takes me about 40mins once a week to clean all tubs, water, and feed everyone. The big secret to controlling the odors is to not cheap out on food (remember the food your feeding your rats is the food your feeding your snakes) and use the pressed wood pellets under the bedding. After my initial setup cost it cost me about $30.00 and 2.5hrs of my time per month. I produce at least 200 rats a month and freeze any extras.
The point of my rant is that it's nowhere near as hard to care for and raise feeders as so many people lead on. With only having 4 snakes I would start off with 2 tubs of 1.2 in each tub and freeze any extras for your f/t eaters to eat later. By having 2 tubs going you'll be able to keep hold backs for future pairings without inbreeding too much. Once you have a good supply of constant feeders you'll find it even easier to add more snakes to your collection while knowing they're eating the absolute best possible. If you decide to go this route and have any questions or need any advice you can PM me directly and I'll gladly help you out.