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These articles should help with that: https://www.gardeningknowhow.com/edible/vegetables/pepper/growing-peppers.htm, https://www.gardeningknowhow.com/edible/vegetables/pepper/how-to-grow-red-peppers.htm

The white areas are sunscald. This is caused when seedlings are not properly acclimated. This article will help you with acclimating them in the future: https://www.gardeningknowhow.com/garden-how-to/seeds/how-to-harden-off-your-seedlings.htm For the first week or two, water daily. Then after that, they need 2-4 inches of water a week.

They are essentially the same as far as needs but hot varieties do tend to do better in drier soil, as they were mostly developed in areas where it is a bit drier. It may be that there is too little water for the bell varieties. It may also be a fungus or bacteria that is attacking the bell peppers that the hot varieties have a natural resistance to. What symptoms do you see on the bell peppers?

It's possible that the culprit is a slug. They normally only come out at night, so you may not ever see them, but the damage is quite similar to what you describe. This article will help: https://www.gardeningknowhow.com/plant-problems/pests/facts-about-slugs-and-how-to-kill-garden-slugs.htm

This article has some thoughts on this problem: https://www.gardeningknowhow.com/edible/vegetables/pepper/peppers-falling-off.htm

It sounds like the feed store did not properly acclimate them and they are suffering from sunscald, which is like a sunburn for plants. They should recover on their own, but you can treat them like they have transplant shock to help them recover better. This article tell how to treat plants with transplant shock: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm