What type of flour should I feed my starter with?
Once my starter was established (started with organic whole wheat flour) I've been feeding it with unbleached AP flour (King Arthur) and that's worked fine. I do this simply because it's the flour I buy in large quantities to stock my pantry, and so it's generally the cheapest flour I have on hand.

If you want to "switch over" to a different flour you can always scoop out a bit of starter a couple days before you bake, and feed it with the different flour. Start with a small amount so you don't have to throw any away; just double the volume with each feeding. I don't usually bother, though.