Just to add my bits regarding rest style APIs because I've been making a lot of those lately:
- sticking with GET and POST may simplify things because they're just a lot more typical and you're less likely to run into odd problems with less well tested lib and proxy support
- a great rule of thumb is POST for writes and GET for reads; this makes it intentionally harder to compose a url that accidentally writes anything
- avoid emitting HTML, the cool kids are letting the browser do all the work now
Some folks will not like the next bit of advice because it's not pure REST. I like to never return http error responses for API level exceptions. Instead I like to provide a "success" boolean value in the json response and a text explanation in a separate variable.