I am interested in down sleeping bag (mummy style) use and care, and have a few questions.

Does the bottom side of the bag usually contain less down? Is there a rule of thumb to determine the "comfort rating" given only single numerical "extreme" temperature rating? Is the foot-box usually the main source of comfort concern while using the bag at the low end of its rating? Does long-term compression actually harm the down, or can the loft be restored?

I'd really appreciate replies to even any of these questions

PS I tried to search around here but the search algorithm thinks "down" is too common of a word and was thus dismissed...