1: Thank you!
2: Warmongering only works to a point if you don't have a very solid economic strategy. I'm not going into detail about it here because it's just not in keeping with the theme of the AAR, but I went into detail much more in my other AAR's on different ways to do this.
3: Defections are actually very rare and quite hard to achieve. You must have very low WE, under 5, which is extremely hard with so many huge armies that can generate so much attrition. You must also drive up your enemies WE to over 15 which is basically requires killing all their forces and occupying much or all of their country. The odds for any given province defecting are very small, and require the province to be a culture other than the primary culture of the nation it would defect from.
However!!! When you're occupying 40-50 provinces for a decade or more and many of them are off culture, the odds of 'some' defections becomes likely because of the huge volume of 'chances'. Buying a lottery ticket is unlikely to produce a win, but buying 5 million...