Hello,
I am an experienced developer (13+years) who worked a lot in algorithm and UI implementation to enhance performances and user experience for industrial software where optimization was critical. I also worked several years using Unity 3D for small projects, mini game jams, essentially creating casual games.
Your project seems already advanced since the graphics are very polished, so it would be my pleasure to propose my knowledge to implement the features you were listing, such as IAP, rewarding system, UI...
The only things that could concern me about this project is the optimization, bug fix and Q&A because it really depends on the quality of the existing code, and how much needs to be refactored to correct the issues. These are really hard to quantify without having the prototype project in front of me. Everything is possible, it is only a question of time !
Besides that, I am confident I will be able to implement the needed features since you provide every sources needed.
Do not hesitate ton contact me for further information.
Regards,
Nicolas Chevalier