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)
The responses in the comments seem to me sufficient to constitute an answer, so I'm posting this to clear the record:
If you want to use the simple past, change the sentence to this: I know that he lived in A before he moved to B last year. Eliminate all that verbosity. Words that do no work provide the brain with cerebral lard & permanently damage the fingertips. – A since-departed (and lamented) user, Bill Franke
You can also omit year in "from year 2011 to 2012": There isn't any possibility of confusion. – kiamlaluno
Best Answer
Yes and yes.
You could use 'had met him when' or 'met him when' interchangeably in this sentence. The meaning differs only very slightly, as 'had met him' emphasizes that it was in the past, while 'met him' emphasizes the fact of their meeting. It's a very slight difference, though.
The only thing wrong with the sentence is 'who is much younger to Mallya'. "Younger to" is not correct because it's a comparative, and that takes 'than' rather than 'to'. The correct way would be '...much younger than' Mallya.