To your first set of questions, nobody knows. The AG's guidance is intentionally vague and won't be clarified until someone gets prosecuted in court. Most here would say to go ahead and bring them in, but you must weigh that against your infinitesimally small chance of becoming the test case.
As for efa10s on your current firearms... I'll put it this way. The State would prefer you register them. The law doesn't require it, though, and I think most of us would agree that in the current climate here, you'd be a fool to do so.
Others will tell you not to move to MA, which is good advice. But I assume that by asking these questions, you've already decided you must. Sorry about that.
eta: the exception, I think, is designed to give you time to get an LTC. If you already have one, it's n/a. Others undoubtedly know more. Though they might not bother responding: as Dean's post gently implies, most of us are GODDAMN SICK of these types of threads.