First figure out your network architecture and how you are going to load balance and support the massive load if it ever takes off. Take out a business loan. Setup up your network. Assemble a team of designers and programmers. Hire a good lawyer. Set up a merchant and gateway account that can handle massive amounts of transactions for a good price and that supports subscriptions. Program, test, launch. Take out another loan for marketing to present the new service to the market that is already saturated and cross your fingers.
My advice is, forget about it unless you got serious cash and you want to devote 100% of your life to get this project off the ground. It is still a long shot.