Hi, Matt here and asking if D3.js library is allowed or not?
If it, then I would help you with creating a custom library with parametrized calls to (custom developed) chart layout functionality using D3.js. I'm not interested in creating completely custom chart library from scratch
D3.js has JSON reading support while REST services are easy to create with PHP (or please explain how you envison REST services to implement).
Looking forward to your reply,
Matt