I'm not sure of the right answer on this. Is it better to have weapons in a broad range of calibers so any ammo you find can be used, or is it better to specialize in a small number of calibers so that you can store/reload the few you might need? I went with a variant of your choice - 12 ga, .45, 9mm, .223, and .22 LR. Whether getting just a few calibers is right depends on why ammo becomes scarce, and I've always been terrible at predicting future trends.
Ditto. I have all of those calibers too, but also .308, .40, .357, and .380.