Great question! Also thanks for your feedback. I really appreciate it :)

As far as error status codes go, it depends on the error/exception itself. If its a client side error then one of the 4XX status codes. If it is a server side error then I use one of the 5XX status codes. The RFC (https://tools.ietf.org/html/rfc2616#section-10.4.2) is a wonderful reference when it comes to picking error codes. I use that as reference to find the best possible fit!