Obviously everything I'm about to say is just my opinion, and as far as teaching others, while I have experience in some areas of teaching, I'm not a member of a bee club and I don't mentor, so I'm coming at this from a rather idealistic perspective. Just my disclaimer.
What I personally do is sugar rolls. I am one of those people who can't stomach killing 100-300 bees once a month in an alcohol wash, and I have zero confidence in passive bottom board drop as a method of determining whether to treat or not. I regularly do deep inspections because I have 10 hives or less and I enjoy inspecting, so whenever I see my queens, which is frequent, I do a sugar roll. I don't test more than once a month, and if it's been two or three months since I've seen a queen or I'm concerned for some reason, I'll take some extra time to look for the queen next inspection and do a sugar roll. Due to the less accurate nature of the sugar rolls, I multiply my mite count from the roll by 1.3 to compensate (a trick that HoneyPump taught me).
As I am foundationless, my bees also make a lot of drones, so once swarming season is over, I cut out my drone brood, check it for mites, and then feed it to the chickens. I do this as an ongoing passive treatment of sorts, another way to get a mite count, and a way to keep the drone numbers low during my big summer flows, since they are just a drain on resources.
My treatment threshold is somewhere around 3% and depending on the season, the size of the hive, whether I'm expecting a flow, etc. I either use FormicPro, OAV, or I do a German trapping treatment, which also gives the colony a brood break. One hive with high counts does not cause me to treat the whole apiary, although it does cause me to keep a closer eye on counts and sugar roll more frequently.
I personally am of the belief that treating without knowing counts and on a schedule is foolhardy. Without knowing numbers before and after treating, I wouldn't know how well my treatment was working. I think that treating when not necessary and on a schedule contribute to mites developing resistance to treatments. As someone who is science-minded, I would be hesitant to take any step without data, and knowing my mite counts over the course of the season enables me not only to know when I need to treat, but which colonies are more naturally resistant, which are the queens I would prefer to breed from (among other characteristics). The only time of year that I treat all the colonies without a prior mite check is if I had several colonies with high counts going into winter. Then I will treat the whole apiary with OAV over the winter.
I am also of the belief that teaching new beekeepers proper parasite management is extremely important. It's a part of beekeeping, whether we like it or not, and learning to navigate treating and doing your own testing and evaluation of treatments is a vital skill to being a good beekeeper. Having someone do something for you is never a good way to learn. I would hope that through instruction and training, new beekeepers would learn to be responsible with their own bees, and ultimately with all the bees in the neighborhood as a result. I'm sure that's far more difficult in practice than theory, but what will happen to the next generation of beekeepers when their mentors aren't around anymore if they haven't learned how to handle this by themselves?