I'm sorry I don't have more to offer you. It sounds like you have been sensible about what you have chosen, given all the factors you have described. I'm going to quibble with you about two things, if only for future reference in case the dike springs a leak. If you do the D3 regimen while everything else you're doing to treat your CH is the same, and you feel that your situation has improved, you can at least tentatively attribute the improvement to the D3, and begin seeing what happens if you reduce some of the other meds. It's not the best situation to be in to play with something that is working, but over the longer run it will be greatly beneficial to you if a more natural, less damaging approach such as D3 works as well as the pharmaceuticals you are using. (I do understand that the "long run" isn't very interesting when you're risking severe attacks right now, so I'm only offering this perspective.)
(It's a strange thing about CH. I was talking just the other day with a fellow who was in remission for a couple of years, which he attributed to the 1200mg of verapamil he was taking every day. At some point, a doctor told him it was going to be very bad for him to keep taking that much verapamil, so he started to lower his doses. As he lowered them, the attacks didn't come back. He's been off all verapamil for several years now, and still hasn't had an attack (full disclosure: he does have shadows every day). I am not saying at all that anything like that could be the case for you. I am just saying how much we don't know about what is actually helping and what isn't.)
Second, I have no desire to convince you to use any substances you don't want to use, but I don't think we've seen anyone here whose life has been taken over by psilocybin and other substances used to treat CH, in the way that addicts' lives can be taken over by "hard" drugs. If you were some day to try this, a substance like rivea corymbosa seeds can treat CH without even giving you any kind of "trip." Since you live in a place where some recreational drugs are legal, you might have seen more "hard cases" associated with psilocybin than I imagine there are . . . and of course the leap of faith to stop the triptans and try "busting" would have to be enormous for you. For some, it has been a "leap of desperation" more than a "leap of faith," and I hope you don't ever get to that desperation point.
(I guess this is a question regarding O2. I'm sure you have thought of this, but I just want to make sure it's said. As a big strong guy, you might well have very large lung capacity. If you are using a proper breathing technique, perhaps even hyperventilating, I can imagine that you sometimes have to wait for the bag on your mask to refill before you can take another full, deep breath. Really, that is the standard for flow rate -- can you use the best possible breathing technique without having to slow down or modify that technique because there isn't enough flow to the bag. If this is an issue for you, then you would want a flow rate even higher than 25 lpm. We have seen some highly fit people need flow rates of 40 and even higher to keep up with their lung capacity. A demand valve system is particularly valuable in a situation like that.)
My best wishes to you. My father came to the US from the Netherlands when he was a boy, and Dutch, not English, was the language spoken in his home here in the US. I'm sorry to say I never learned any, but I do still feel an affinity toward folks from my ancestral home.