I think you need over 4,000 in D3 for the danger level, but yes, I would stay below that. See
https://www.livescience.com/42481-vitamin-d-supplement-facts.html
We all got the endless message that excess Vitamin C washes through your system.
Other Vitamins don’t do that and have toxic levels as you point out. But this is best measured by a Doctor in blood tests rather than just dosage levels. Some people, like me, have special needs so I get monitored and vitamin supplements checked out by nutrionists working with a Doctor.
Zinc has an upper safe level as well. We all need to stay well informed, not just from some website.
People have to distinguish between fat-soluble and water-soluble vitamins, as well. The latter generally ‘wash out’; the former generally build-up.
However, even some of the ‘wash out’ vitamins - the ‘B’ complex, especially - need to be taken in certain ratios to one another, or complications can arise. (This is why you will see bottles of B vitamins in the drugstore calling themselves ‘balanced’.)
Minerals can be complicated, too.
But none of it is ‘rocket science’ - you just have to find good, recent books and studies on the subject.
(Not a doctor - never played one on TV.)
Love your comments on civil engineering and such but 4,000mg D could kill not just one, but a bunch of people if distributed among them. They would excrete nearly all the water in their bodies, among other issues. Don’t try this at home! Units of measurement are important, as I’m sure you’re aware in your own discipline.