I'm curious if you made any progress on this. I did take a look at the spec, but there's a lot to read there and I've been pretty busy with other things.
I've helped a few others with projects like this, but what I've typically found is that the biggest time sync is access to tech support and to a test server that provides reasonable feedback. It's not unusual for there to be errors or ambiguities in the printed ref (despite what would otherwise seem like extremely formal documents, i.e. for credit card processing, insurance claims, etc.), or some kind of assumptions that aren't explicit, and then it takes days and dozens of phone calls, emails, etc. to get a simple answer.
