<< "How long should the avg fridge / freezer (top and bottom) last before needing to get cooled again?" >>
In my experience, 6 hours is the best you can get. After that, you should view highly perishable items with a skeptical eye.
When you get power again, fill every nook and cranny with water jugs. Cover the exterior with a blanket when the power is off.
<< "Ice Cream never melts here when the power dies." >>
Correct. The calories don't count either. It's an emergency.