the choice between male/female is a hard separator between fetishes. what I mean is you're really choosing which fetishes you're gonna cater to rather than the MC. which obviously also means you're choosing your audience. very difficult to switch after choosing gender. in this trans-anything falls on the female protagonist side.
excluding that, best by test is to start with a failed, faulty character. which both gives you an obvious character arc, but also everybody roots for the underdog. where as 'the winner' is the worst place you can start from, UNLESS your story is about beating that character down and ending it in his miserable and undeserved death.
what people here often mistake as an aspect of a loser MC is really the writer failing to make him likeable. doesn't matter how much of a shitbag the MC is, he should always show some glimpse of goodness which allows the player to overlook the horrible choices he makes. if that glimpse isn't there, people will just hate him. you don't want to play with a character you hate.
so when you build up your pervert MC, make sure he sometimes does the odd self-sacrifice without expecting a reward. random acts of kindness in the midst of his downward spiral to depravity.