Payment Gateway Webapp

I am planning to implement a payment gateway web-app, much along the likes of [login to view URL], google wallet, and paypal. What i want to initially implement are: - Registering users (using 2FA and social logins) - Verifying users identity after registration, using picture ID or (Name, address, last 4 digits of SSN) - Integrate with payment gateway (Knox payments or Synapse Pay) - Both have API's already built. - Allow users to link a U.S bank account - Deposit from bank account to wallet - Cash out (withdraw) to linked bank account