It all depends on the person and the caloric needs. Personally, I would not go below a 500 calorie deficit. So if you needed 2700 cals in a day, you should be shooting for 2200 cals.
This is an question that can't be answered. Everyone's caloric needs are different. It depends on your current stats, metabolism, macros, energy expenditure from cardio/exercise, and how much time you have to reach your goal.