The amount of weight loss you’re talking about may leave a small amount of redundant skin, but also you’re very young and it’s possible as you continue to loose weight your skin will rebound well. My suggestion don’t worry about your skin yet, focus on lifestyle then when you get to your goal ev...
Fat necrosis is not considered normal, but it is a risk of the surgery. I encourage you to work closely with your surgeon to address your concerns and alleviate the pain. If you are interested in a more sculpted result you may want to consider a tummy tuck.
Typically multivitamins can be used pre and post operatively. However this question is best answered by your surgeon who is most familiar with your medical history and the details of your surgery.