Well, to get the terms right, a man or woman, who transitions to the other gender, is usally called a trans. A trap is usally a boy/man who looks and acts feminine, but doesn't intend to transition. A futa is usally a character with both genders, meaning with breasts, dick and vagina. Balls are some kind of optional, depending on the taste of the dev and the willingness to model them. The term futa gets often misused by people for characters, that are born with breasts and dicks but no vagina. The misuse has evolved through porn and western ignorance and gets justified by "not having the same psychological struggle, that a trans person has". For the lack of a better term, I usally call them chicks with dicks or dickgirl. I hope, these infos can help to give you an idea, how you want to handle that character.