An HTTP response has no size limit. JSON is coming as an HTTP response. So it has no size limit either.
There might be problem if the object parsed from JSON response consumes too much memory. It'll crash the browser. So it's better you test with different data sizes and check whether your app works correctly.
I think lazy-loading is the best approach for such large amounts of data. Especially when dealing with object literals.
See High Performance Ajax Application presentation from Yahoo.