1- The Mahr can be anything you agree upon. It can be money, it can be a gift, it can be a meal, it can be anything. It has to have monetary value. You can pay it whenever you are able to. Or you can make a bank transfer, or send with western union or paypal. It can be any amount.
2- No. Once the Mut’ah contract has been done, it won’t be a sin to have such thoughts.