I worry about temperature within the hive because the bees regulate it quite effeciently. Regardless of the temperatures elsewhere in the hive the bees always keep the brood chamber around 90 degrees. If the brood isn't covered with nurse bees they will get chilled and die, a condition called, appropriately, chill brood.
Bees do not have to occupy capped honey cells but the eggs, larvae, and pupae must be covered with nurse bees continually. The same goes when bees are building combs, if there is not enough bees in the hive to occupy the available space they won't draw comb where they aren't.