Method of Salaah

Q: How long does the Aa in Aameen have to be stretched for?

Q: In Ruku are the elbows meant to be tucked in or sticking out?

Q: When sitting in qaeda position where does one look? At the hands, knees or lap?

Q: When having risen from Ruku, does one recite Rabbana Lakal Hamd or Rabbana Walakal Hama (i.e. with the و or without the و)?

Q:

1. I have been told that if, for example one reads surah Nasr in the first rakaat, then in the next rakaat one cannot read surah Ikhlaas - it has to be the next surah, or a gap of 2 surahs. Please clarify this rule for me (e.g., does it apply only to short surahs, does it apply to 4 rakaat salaah as well, etc.)
2. For long surahs, can one read from different parts of the surah in consecutive rakaats. Eg., 1st rakaat beginning verses of surah Najm, and 2nd rakaat ending verses of surah Najm.

Q: Can a person read the following Dua in his Fard Salaah:  حمدا كثيرا طيبا مباركا فيه after reading: ربنا و لك الحمد, in ruku', similarly can he read in jalsah: اللهم اغفرلي و ارحمني و عافني و اجبرني و ارزقني and if he is a muqtadi can he read these two dua's?

Q: If "Rabbanaa lakal hamd" the word hamd at the end is sounded as a ت and not د will the salaah brake? The letters ت and د are they from same makhraaj, and so there is no zallatul qari is these are replaced by eachother not on purpose?

Q: I read in a book that to read Sami Allahu liman hamidah, to read hamidah with a soft h i.e. a ه will break salaah. Why is that? The meaning is changed? What if it happened unintentionally?

Q: Question regarding reciting inaudibly. In my case I was praying Dhuhr Fardh and quietly as to hear my own voice, in my last (4th rak'ah) - I was reciting "Ghayril Maghdoubi" at Maghdoobi, I could only clearly hear "Ma--doobi" the Gha wasn't proper so that I could hear, but I moved my tongue to recite it as normal. Obviously I didn't want to recite "Ma--doobi", so I think I inaudibly said the gha, does this matter or affect the validity of the namaz?

Q: What is the اصح (most correct) opinion regarding when to start takbeer-e-tahreema? 

1. After raising the hands
2. While raising the hands