I agree a double negative is a positive. Acceptable exception being when being said clearly as slang or for emphasis.

You make a point I've never considered. Strictly speaking, you're correct: to "badly miscalculate" is to do so "poorly", and therefore, "not to miscalculate at all", or "not to miscalculate so severely". However, the word "badly" is used so often from a young age, I think, no one would ever criticize you for using it in place of "severely", which, as you say, is one of degree.

I agree the colon precedes a list, but a list composed of at least three items. In your example, the colon would seem to be too strong. However, I don't have a citation or formal support for my position.

In legal documents, to be extra clear, I often use a colon, and plus, I would add numbering, like this: "I have two (2) sons: (i) Bill; and (ii) Ben."

I am unaware of the "different from/to/than" debate.

In your three examples, the second is by far the one I've most commonly heard.

"Separate to" I can see, but "deal to"?

And I can see "think to" followed by a verb, whereas "think of" is often followed by a noun. Still, I more commonly use "think of".

What about regional differences - "quarter of" vs. "quarter to" (15 minutes before the hour)? I'm used to using "to" in this instance.

Bas Aarts, in his "Oxford Modern English Grammar" advocates an approach that is adaptive and that evolves, rather than a stricter or prescriptive approach. I suppose the key is to understand and to be understood.

I remember being taught some grammar by the nuns in Catholic school, but the bulk of my grammar knowledge came from my father, not from school. And the kids in my class(es) were never any good in grammar anyway, so that's a sad way to say that we didn't have far down to fall.

I agree with you and you make a good point at the end, as in the British way, you cannot distinguish whether the plural usage indicates one school board composed of multiple members or multiple boards.

I would argue for a hybrid: “She didn’t realize … until she smoked 10 cigarettes a day.” The smoking of 10 cigarettes a day is a milestone or a marker in this smoker’s process/evolution. The realization happens suddenly. Once the smoker hit this milestone/marker of smoking 10 cigarettes a day, the realization hit her. The word “until” already signals the sequence of the events, and therefore, it is not necessary to use “had”.

In addition, to me "had" serves two functions: 1. as the past perfect, and/or 2. implying the act (verb) is a lengthy(ier) process.

I accept the use of "My Walmart" to mean the Walmart closest to my home, and I also think it's prudish to object to that usage.

However, I would also point out that "My Walmart" can have at least four possible meanings:
1. that Walmart closest to my home;
2. that Walmart closest to my work (I often leave from work to go elsewhere);
3. that Walmart that I visit regularly, regardless of its proximity to my home/work; or,
4. that Walmart that I prefer, regardless of its proximity to my home/work.
(I often visit an out-of-state Walmart as I enjoy it and I visit it when I am visiting my out-of-state friends.)

I accept the use of "My Walmart" to mean the Walmart closest to me because: (i) I myself use it that way; and (ii) I often hear others use it in that way. And, I do believe it is prudish to object to this usage.

I would add one more distinction: "My Walmart" can have at least three meanings that I can think of:
(a) the Walmart closest to my home;
(b) the Walmart closest to my work - as I myself often go from work to other places; or
(c) the Walmart I visit regularly, regardless of its proximity to my home/work, as I often visit friends out-of-state and I enjoy going to the Walmart near them.