Agree with number one - these characters also having to watch their weight would be cool. Although it should be ultra hard to convince them to dine or gain with you.
Disagree strongly with number two - that would take too much control away from the player, DDD should be a strong monopoly!
Disagree strongly with number three - girls changing their personality would be super confusing and you may end up with a lot of characters with the same personality after some time.