There is a frequent DIS poster who will probably come along and answer more specifically.
What the Guidebook for Guests with Disabilities says is to contact the CM at the entrance to get the reflective panel and be seated in the correct area.
I don't believe you need to make any reservation for it (because of what it says in the Guidebook).
The phone number listed in the Guidebook for assistance/schedule of interpreted shows is 407) 824-4321 [voice] or (407) 827-5141 [TTY]. I'm pretty sure they could answer your questions about reflective captioning too.