When cutting, the body likes to try and keep its body fat stores. Thinks it is starving, and would use them as a last resort for survival. Muscles consume the most Calories, so the body will use them up to try and protect its key organs.
Fats are not the primary energy source inthe Body. Carbs are.
Really depends on your body at the time. If you go into a gym after just waking up and start working out, maybe the first 10-15 minutes would be glycogen, but you wouldn't have any left, and thus would would force your body into using fat. muscles store gylcogen, so does the liver. But there's a certain amount, and liver glycogen is NEVER used by muscles.
yeah, depending on diet/time/last meal/last activities is all i'm saying. but protein is last on the list to be catabolised.