@chitty if you are planning to have this be a US based business, I would advise you to look into the history of microlending, specifically with Prosper. I was an early adopter on Prosper, before the SEC ruled it had oversight. Prosper was hit with fines, registration and reporting requirements and so on which severely hindered it for a number of years, eventually causing it to lose its dominant position to Lending Club.
I would imagine you'd have to register with them and have a number of hoops to jump through, so I would consider basing it in another country. Also take a moment to sit with an attorney to get their perspective.
I wouldnt do it in the U.S. and I would basically copy the already existing P2P bitcoin models.
Some of those Bitcoin P2P models are already struggling due to regulations. BitLendingClub for example closed down citing regulatory pressure. BTCjam had to abandon major markets, locking out users from certain countries. I do think crypto P2P lending will win out in the end, but it's challenging fighting in a domain where the state (and banks) assert control today.