Method of Salaah

Q: I started praying magrib alone before another brother joined me, so during the second rakaat I recited only one verse from the Quran (sura ghafir verse 44) after fatiha and went to ruku position. Since then I have been having doubts if my salaah is valid or not. If not what should I do because that brother is gone now. 

Q: When we end the salaah by saying assalamualikun warahmatullah to whom we say it and where should our gaze be?

Q: I read a book called Umdat ul Islam written by Abdulaziz bin Hamidullah in Persian some 700 years ago that if one reads the word hamida of sami Allahu liman hamidah with the letter ه instead of ح the salaah becomes faasid. Is this correct, it was also written that if you read Allahumma salli, the word salli with a س and not a ص the salaah is faasid. 

The book in question is it a authorative book? It says also some strange things like that in Jami al Fatawa it is said that if a person makes zina with a animal the animal should be killed and burned, and the person should also burned or a wall should thrown on him.

Q: When I make sajdah, I am not satisfied and I push my head too hard. I want to know the correct way of making sajda. How much pressure is requried? Where exactly should the floor touch the nose and forehead? Anywhere or some precise position is required?

Q: In my namaz whenever something comes in my mind, even if I try to regain my concentration I forget what I read, in which rakaat I am and many other similar things. What should I do? 

Q: Must one make sajda-e-sahw if one misses the ruku in the last raka'ah in witr?

Q: I would just like to get clarity on a few aspects of Salaah (hanafi).

1. What is the correct way of performing ruku, does one say Allahu akbar first and then bend down, or does one say Allahu akbar in the motion of bending?
2. In witr Salaah, does one drop their hands and then raise it for dua Qunoot, or can one raise their hands directly from the folded position?
3. After salaah, I know it's sunnah to say Astaghfirullah thrice, is it also sunnah to say Allahu akbar once then astaghfirullah thrice?
4. Is salaah valid if in a 4 rakaats fard salaah, after surah Fatiha of the 3rd rakaah, you say just 'bis' of Tasmiyah before realising you don't read a surah now? If it is valid, what is the maximum length of Tasmiyah which may have been recited mistakenly without invalidating Salaah?

Q: Is it a Sunnah after fardh Salaah to read Allaahu Akbar once and 3 times astagfirullah. The Third astagfirullah should be recited audibly and pull on laah?

Q: If one omits the Tasmiyah before Surah Fatiha in the 2nd, 3rd and 4th rakaat of Salaah due to habit, will the Salaah be acceptable? When we read Salaah with Jamaat, the Tasmiya is always silent and unfortunately I developed this habit.

Q: When performing Salaah behind the Imaam, in the sujud after saying a few times "subhana rabbiyal alaa" somehow I was about to say "sami Allahu liman hamidah" but as soon as i said "sami Al" I realisized and cutt off and continued saying "subhana rabbiyal alaa". Now was my prayed invalidated since I cutt of at the half? Must I repeat it?