Sourcing An Image Sensor?
Even at volume Sony is not always interested in playing along :)  The higher you go in resolution/performance with image sensors the harder they will be to get.  The good stuff will all require an NDA, which will mean they want to look at your business to see if they even want to engage.

I would recommend you start with modules like you say.  I don't know the iphone camera but I'd wager it's either a SLVDS but more likely a MIPI interface which you can read about online.  

Interfacing to a raw image sensor takes more than just connecting to the camera the hard part is the image processing of the raw data, the adjustment of the 100s of registers in the sensor (often per frame), and the tuning to make a video that looks decent :) 

Have you considered the Rasberry PI and it's camera for your project?  That might be a good beginner way to go.

Last piece of advice, build your project so that it's useful to people using parts you can get.   Don't worry about mass production worry about getting 1 customer, or 10 customers that's even harder than scaling...