Your use of "wanna" displays informality instead of impoliteness. For example, a high school student will most likely use it with his peers to suggest a trip to the mall (e.g. You wanna hangout?) but a lawyer would almost certainty not use it for a closing argument (e.g. The truth, if you wanna know...). If he does, he will come across as being rude and disrespectful to the solemn nature of a court, but more importantly, he is frowned upon because he shows disregard for the place, audience, hierarchy, formality and purpose of his speech — the register.
"Who do you wanna help you out?" It sounds clumsy to use "wanna" here because the word "you" is used twice: "Who do you wanna" = "Who do you want" refers to someone you have in mind. At the same time, "wanna help you out" = "to help you out" refers to the intention to assist you.
Phonetically, it can already sound confusing if you say, "Who do you want to help you out?" quickly, more so if a slang is used. It would be better to simply ask, "Who do you want help from?"
I hope this helps.