Two questions, kcal per day and belly flap question.?

I can't really help you with the calorie part of the question, but at your age you shouldn't have much of a problem with the excess belly or loose skin in that area. Just make sure you're getting enough water. 2.5 kg sounds like a bit too much per week, though...you might want to slow that down because when you lose a little slower, you have a better chance of keeping it off.