No you do not need to be a TR guest (many diamond members are locals)
The list changes a bit monthly (but not much). In May, Tony & Tina's wedding wasnt on the list, but back in July; I just saw the Oct. list & it was still there.
50 Shades is closing Nov. 15.
The key is to go the DAY you arrive; you will find the most popular shows sold out that day (well, sold out for free diamond tickets)--Penn & Teller, 50 Shades and Tony & Tina (since it has dinner, too?) are often sold out. But you can get them for other days in your trip.
Additionally, if you can schedule your trip over 2 calendar months (as we did--the last weekend of May into the first week of June), you can get a pair for EACH month. Nice.