1) So, once a person makes it to a stage, they will always cycle through the stage they've made it to and the previous ones? For example, say someone makes it through the three characteristics, they will then continuously cycle through mind and body, cause and effect, and three characteristics rest of their lives (unless they make it to a further stage)?
It varies depending on where you are, pre-Path you'll cycle from 1st ñana to your current "cutting edge" depending on where you've made it to at that point. Once you get 1st path, and until you start the cycle for 2nd path, you'll cycle from A&P to Fruition.
2) How fast do pre stream entry folks cycle through these stages? Do they cycle even if not on the cushion?
I did a lot of different practices before getting stream entry, none of which were vipassana proper and none of which were within the Buddhist model of things so my take of this may a bit different to those who've gone the insight route from the start. In my experience, cycling happened and I was aware of it ever since the first time I crossed the A&P which, like lots of people, I did without any training or experience with meditation. It was only on finding MCTB that I found out about the maps, stream entry and all this insight stuff and went "Oh, right so THAT'S what was happening". In terms of how quickly pre-Path people cycle, it's likely to depend on a variety of factors so I suggest just being aware of how it happens for you.
3) Is there something about the dark night which is different, such that, once you make it there, you don't cycle through mind and body, cause and effect, three characteristics, and A+P anymore, but only cycle through dark night? Meaning, it becomes a new baseline, or is the baseline always mind and body?
No, only after Path do you cycle from A&P up to Fruition and back down. The baseline is whatever stage you're currently in, don't worry about trying to figure out where you are as repeated cycling through each stage will make it abundantly clear over time.
3A) Or, do you continue to cycle through the earlier stages but don't really notice them much (note -- wouldn't you notice going through the A+P again and again since it is associated with weird effects?)?
Yes, but how much you notice them will depend on how strong your concentration is and how closely you're paying attention to what's going on, on a moment by moment basis at the sensate level. It's worth knowing that the A&P doesn't always happen in exactly the same way, sometimes it passes really quickly without incident and sometimes it kicks your ass. Don't
expect things to happen the way you've read them described in someone else's words, it's all there in your own experience if you pay attention to it.
4) Once past the A+P, the stages begin "happening to you," such that, the dark nights stages of 5-10 will happen regardless of whether you meditate or not?
Pretty much, yes. Think about it this way: Seeing the arising and passing away of the whole fabric of reality, right in front of you in the most undeniable and direct way, makes people realize that things aren't what they thought they were. That sort of shakeup in worldview can be quite earth-shattering to some and lead to difficult times as they begin to question everything they've ever accepted as true. Dark Night is a convenient, and oddly accurate, way of describing what usually happens after a big 'spiritual' experience.
5) Say a person is a dark night yogi -- after unwittingly going through the A+P when 17 years old after taking acid, or an extreme masturbation session, or a particularly frenzied rave dancing session, etc. -- does this mean they basically only cycle through stages 4-10, or is it 5-10? Also, how fast does this cycling happen? [I mean, does a person go through misery alone for years, or minutes?]
How they got there isn't a big deal, what's going on right now is what counts. As I've said, the factors which cause cycling to happen quicker or slower will vary for each person, but I think that a solid and regular meditative practice will almost certainly help.
5A) Clearly, I would consider myself a dark night yogi at this point [500 trips of acid back in the 90s, anyone?]; however, I am much more functional and positive and happy now than I was, say, ten years ago (although I've yet to make it to equanimity). Can someone basically solve or get a handle on the dark night stuff without having gotten to equanimity? Meaning, is there something to "solve" in dark night, or is it truly just happening to you without any ability to control it or master it (pre stream entry, that is)?
Dark Night, in my experience, comes down to learning to surrender to what's happening. Stopping trying, let things be and accept things as they happen because this will lead to equanimity, people want to fight with Dark Night and try to control the unpleasant sensations which might show up but that just leads to more tension and suffering. There's nothing to "solve" in Dark Night, it's just another stage of the process which pretty much everyone will experience to some extent, don't let it become a big problem that you need to do something about 'cause that's the opposite of what needs to be done. With sufficient acceptance and the ability to discern the three characteristics, Dark Night can be considerably more pleasant and easy going than you might think.
6) If you are a dark night yogi, you can still have a new A+P (if it has been a long time since the last one)?
Yes.
Hope that's of some use to you.