I am a young entrepreneur thinking of developing an e-wallet like PayPal or wepay in China, but in a different philosophy... I want it to be an e-wallet, as well as a bridge for payments, where stores only need to integrate our e-wallet payment system to be able to accept all kinds of credit cards and cash services which we integrate into the system. I would hire expert developers when it comes to programming, but I would appreciate any insight or advise when approaching ecommerce business.
If you want mass adoption like Paypal and Wechat, I would say make your e-wallet customer-centered. Make it as easy and secure as possible for your user to do transactions and send money to their friends. Once you have a lot of users, shop and ecommerce owners will naturally come to you.
As for the financial side, I would also model Paypal and their fees structure to start.
Good luck with your project!