(Sorry if my programming roots are showing.
I've just spent a few head-spinning, mind-numbing hours reading dozens of websites about the best way to store a sd culture so it can be revived most quickly. I am posting the following information in the hope that it will either be confirmed or corrected by those who know better.
Let's start at the point where you have just taken your starter out of the fridge to bake a pie. You start feeding it with flour and water until you bring it to peak condition. (How long this takes is what I hope to minimize by always keeping as active a batch as possible in the fridge.) Once you have brought your starter back to full strength, you should put aside about half a cup,, then feed it with 1/4 cup of flour, 1/4 cup water, and let it sit out for a few hours until it is peak-y, and then into the fridge goes one very happy cup of sd culture.
It seems like there is no reason to keep more than a cup of starter in the fridge. It will require less volume in terms of feeding, and (at least for making a couple of pies) you will have plenty when you have brought your starter back to peak and are ready to bake.
Now (here I am on very shaky ground) you should be able to let your starter remain in the fridge for 3 - 5 days. Then, every 3-5 days, take it out, dump half of it out, and again add a 1/4 cup water, 1/4 cup flour. There are two bits of fog here: 1) is it necessary to bring the culture to room temp before feeding it, or can you just plop in the flour and water, stir, and back in the fridge? 2) Several sites recommend tripling or quadrupling the amount of starter via feeding. That is, if you are taking a quarter cup of starter out of the fridge (or taking a larger amount out but dumping all but 1/4 cup), you should feed it with 3/8 cup flour and 3/8 cup water for optimal results.
By feeding your culture once or twice a week, you will be minimizing the amount of time it takes to bring your culture back to peak strength.
Does this make sense?
I am also wondering whether you could keep a starter on your countertop indefinitely if you were to feed it once a day.