1.
The first question is about the tense we should use after "as soon as". In a sentence such as this:
I had left when the phone rang.
you need to use the past perfect in the second clause to show which action came first and which – second. However, when you use “as soon as”, the sequence is clear and it is normally a matter of preference which one to use, so both your examples will be correct. In American English the preference would normally be past simple. The past perfect would emphasize the fact that one action was complete before the other one occurred. (an explanation given in Grammar for Teachers by Andrea DeCapua)
2.
In the second pair of examples they are both correct again. It is unnecessary to use past perfect because the time is mentioned and the sequence of events is clear. Also, the actions are described in the order in which they occurred. You can use the past perfect if you want, to emphasize that one was before the other.
3.
The third question was about the sentence
He said that the moment he first met her, he felt something special and began to keep a diary.
The actual words the man said must have been:
"The moment I first met her, I felt something special and began to keep a diary."
When you report his words and begin with “He said”, the entire phrase shifts one tense back and becomes:
He said that the moment he had first met her, he had felt something special and had begun to keep a diary.
Although this is the grammatically correct sentence, it is very common that the past simple does not become past perfect in indirect speech. When reporting, native speakers tend to make present tenses past ("I am studying" - "She said she was studying") but very often do not care to make the past tenses perfect, as grammar books always teach us we should.
That is what makes both these sentences correct: "He said that the moment he first met her, he felt something special and began to keep a diary." and “He said that the moment he had first met her, he had felt something special and had begun to keep a diary.” (have a look at the end of this page)
It is perfectly natural to use the past perfect in she had grown up. The past perfect summarizes all that came before in her life, even if this was a process, up to the moment in time that the narrator utters those four words.
What is awkward is to link "she had grown up" with verbs that are not in the past perfect. Thus, both
She had grown up, and it was said that she became a barmaid, kind and generous.
and
She had grown up and became a barmaid, kind and generous.
do not link with precision the clause she had grown up with the actions of the rest of the sentence. The second version is especially jarring. I can hear an almost audible clank when I read that sentence. To take full advantage of the conjoining nature of and, both actions will be cast in the past perfect:
She had grown up and (had) become a barmaid...
The first sentence is not as bad, probably because the intervening narrative and it was said that (or even the active and people said) connects she became a barmaid in some nebulous time relationship to she had grown up. The only thing we know about when the entirety of and it was said that she became a barmaid is that it is after the moment expressed by she had grown up. But years, decades could have transpired in between. Thus, unless one enjoys living in such a nebula, even the first sentence can be tightened by using the past perfect: and it was said that she had become.
Best Answer
Your teacher is quite correct: could, might, should, would are the 'past' forms of can, may, shall, will. The example your teacher gave you is perfectly OK; you would also use these forms to backshift present-tense forms in reported speech:
Must has no distinct 'past' form; historically, however, it is the 'past' form of a verb which has lost its present form, mote.
And that's a process that's still going on today. Shall has almost disappeared from Present-Day English, except in legal contexts, and may is in steep decline. Must is very little used now as a past-tense form; some teachers even tell their students that had to must be used instead. Similarly, past-tense could and would are giving way to was/were able to and was/were going to.
I suspect that what underlies these usage shifts is that the so-called 'past' forms of verbs don't always signify backshift—past-tense reference—but are also used to signify what we might call 'sideshift': a less assertive social or logical modality. This is especially true with the core modal verbs, which are the primary indicators of modality; the 'past' forms of these verbs are used so frequently to signal social or logical distance that the use for actual past-tense reference has become secondary. Except in the most formal registers, could, might, should, would have become almost (but not quite) disconnected from their present-tense forms.