Obviously, you have confidence in the sugar roll method but I have heard others express differing positions on it. I'd like to know more about the pros and cons on it. Or the whys and why nots, however you want to put it.
A sugar roll is not as accurate as an alcohol wash, so I multiply my results by 1.3 to make up for that difference in accuracy. I find the sugar roll easier and it doesn't require me to kill bees, so I prefer it. I like to do sugar rolls regularly because I'm someone who likes data, but I'm honestly moving away from treating based on sugar roll numbers alone. I'd rather treat colonies with high mite loads who also are showing signs of stress, because I'm trying to breed for not only resistant bees but resilient bees. That's my take on it anyway.
What causes a brood break and how long do they last?
Anything that causes the colony to be queenless, and therefore broodless, for long enough that all the capped brood has emerged causes a brood break. In this case, the queen in this colony had become a drone layer over the winter, so I pulled her in my first inspection of the year, but for some reason it took several weeks of me adding donor frames of eggs before they made a new queen, and therefore their population got very low. I debated combining them with someone else, but it's early enough in the season that I decided to just let them go.
And lastly, we are still having spring here so our weather is above and below bee flying weather. What do they all do in there when they have no-fly days?
Well the bees who are of inside work age just do their inside work like always. I'm not sure about foragers, but I'd guess they will sometimes just rest or maybe help with guard duty. I opened a hive once on a rainy day, I can't remember why, and there was a cluster of bees just hanging on the underside of the lid, who I think were foragers just hanging out there because they couldn't go outside.