1)Need to create unlimited wallets for users and can make transactions of their bitcoins in their wallet to another bitcoin address.
2)Send/receive bitcoins,check balance and make a perfect transaction between 2 users and many.
3)No need of UI ,just basic is fine.
4)Need to integrate [url removed, login to view] API ,you should have previous experience with Coinbase API methods and Ruby on rails.
Have low budget of 20$ but will lead into long term for successful devs.