Hi,
I am a full stack developer with more than 12 years of experience. I am interested in working on this project. My experience in eCommerce websites and platforms will help in this project I think.
From the description I feel that you have a website which acts as the "Bank" or place where users can register for their account, then "earn" coins and spend on other two sites. This project, I would like to divide into N modules.
1. User registration module where the user can have an account with website
2. The "accounting module" where users can have coins earned
3. A login API with which the users can login to other site using oAuth (Open Auth, the standard that is used by people like Facebook)
4. A payment gateway - like the creditcard gateway, but little inferior to that so that people can use coins from website 1 to other
5. Integrate site 2&3 using APIs we built.
The accounting module needs a reports module so that users can get a balance statement.
I think I can do this in given budget and time. Looking forward to work with you.
Regards
Varghese Chacko