Who for people, which for things. When the relative pronoun wh~~ is the subject of its own clause, who/which. When it is the object, whom/which. 'The man who left his door unlocked was burgled'. 'The door which stood open was ...'. 'The burglar whom I saw coming out was ...', 'The bag which he was carrying was ...'.
When we want "of whom" or "of which" a handy word is "whose" for people or things. JK Rowling's "The cabinet whose doors bore ..." is absolutely fine.
"To whom" and "to which" are for when the pronoun is the indirect object.
Please note that the word "that" should not be used as a relative pronoun, and if you try to use it after "of ~~" or "to ~~" it proves that it is not a relative pronoun, because you can't.

Who for people, which for things. When the relative pronoun wh~~ is the subject of its own clause, who/which. When it is the object, whom/which. 'The man who left his door unlocked was burgled'. 'The door which stood open was ...'. 'The burglar whom I saw coming out was ...', 'The bag which he was carrying was ...'.
When we want "of whom" or "of which" a handy word is "whose" for people or things. JK Rowling's "The cabinet whose doors bore ..." is absolutely fine.
"To whom" and "to which" are for when the pronoun is the indirect object.
Please note that the word "that" should not be used as a relative pronoun, and if you try to use it after "of ~~" or "to ~~" it proves that it is not a relative pronoun, because you can't.

I do not know which writers have been using 'was' and 'were' interchangeable (sic) for all those 300 years, but I like your neologism "ideolect", which my dictionary, like me, is too old to include. So too "counterfactual". I shall check them on Google in a few minutes. They have never seen the light of day in any of my language lessons, nor in the textbooks I have used.
Your point about verbs other than 'be' is well taken. The problem with the English subjunctive is that its conjugation is so much like that of the past indicative, it is really only with the rare irregular verbs such as 'be' that its different form is apparent. As it is apparent it is easy to notice it, learn it and use it, so use it!
"If I was a rich man", as quoted by a contributor, sounds obviously plain wrong because it is plain wrong. English dialect maybe, but it is not standard English.

I don't think it needs an education in a decent UK school, just a decent school - German and Danish friends do not get this wrong when speaking in English, because they have been taught the English version of their own languages' subjunctive forms for use in closed conditional clauses (putting forward an impossible hypothesis), such as "if I were you". I cannot imagine having heard 'if I was ...' used by anyone using English as a second language. Americans get this one right too. It seems almost a deliberate ploy to suggest such things as "if I was you" when used by a British public figure, with what motive? The answer is evident.

A nice question but there are other words which have to have negative connotations: could you be mayed if you saw something gusting? Or dismayed/disgusting?

If "notice of two weeks" is an alternative, then "two weeks' notice" with an apostrophe is correct. Genitive case.

Hey, goofy, a gerund IS a noun, that is why it is a gerund and not the verb it looks like and came from. it has verbal qualities, but it is still a noun, so "My writing is improving" is correct.

Why must we add the word "the"? What does this lend to make the sentence better? It makes it a nonsense, surely?

They do not appreciate my singing the national anthem.
*They do not appreciate my assistance the national anthem. What's the difference? You can sing something, like a song (object, so transitive verb) but you cannot assistance something (so intransitive) so a poor example, I fear, of how to explain a gerund as a verbal noun and how it works. "My singing .." is correct, by the way.

Perhaps it would help to think about whether it is the running or the time it took which is what you want to accentuate. "He ran for 12.2 seconds in the 100m" emphasises that it was the 100m which matters,and the time is not of interest, "He ran 12.2 seconds in the 100m" emphasises the time taken.