I am guessing your app is not WhiteHat so I would be very cautious with what you do with it because once it's killed, you just lost all of those users and you're back to square one.
If I were you, instead of essentially handing this over to someone who might or might not have more experience, I would personally build up smaller apps and gain the experience yourself through trial and error. I am not trying to say there is anything wrong with a JV if you would like to go that route but if you have an app with that many users, you are already doing something right. I would definitely start performing a lot of trial and error, take notes, and come to your own conclusions. It is the best way to learn IMHO.
After you have accomplished this, the sky is the limit (scale it up).