Sajda-e-Sahw

Q: What is the ruling for a masbooq who forgot to read a surah after surah fatiha but completed his namaz?

Q: I performed my Zuhr fard salaah. In the qa'dah (sitting) after two rakaats, I recited the tashahhud, durood and the Dua. Then I remembered that it is a four rakaat salaah, and without making salaam, I stood up and continued and completed the Salaah. However, I did not make sajdah-e-sahw. Is my salaah valid? 

Q: Although there was no need to make sajda sahu, one inadvertently makes sajda sahu in salaat. Is the salaat valid or does it have to be repeated?

Q: During Salah, if one recited a particular Surah after Surah Al Fatiha in the first rak'ah (for example, one recited Surah Al Kauthar), and then in the second rak'ah, after reciting Surah Al Fatiha, one begins to recite Surah Al Kauthar and then realises that he has already recited this Surah in the first rak'ah, and so he immediately starts again by reciting a different Surah (for example, Surah Al Ikhlaas). Does this action require sajdah sahw, since he was reciting a particular Surah, then stopped, and started again by reciting a different Surah?

Q: I prayed asr or Dhuhr I think, and I think in 2nd rak'ah I said ayah of al Faatihah wrong but was not sure so I ignored it and on the third rak'aat I noticed it was probably wrong so I took the 3rd rak'aat as 2nd and finished like normal and then did 2 sujood sahw. Any thing wrong with this?

Q: In Salaah, I recited in my last rak'aat  "Ihdina siraatal mustaqeem". But when I tried to do the Qaf with kasra it was like kaaf and so I recited it again, but this time the ta in Al-Mustaqeem was not properly audible I think, but I moved my tongue to say it and I guess I now think the second time I recited it, it was acceptable - but at the time my mind was like blank, I thought of both carrying on and saying it again and as I was quite pressured because I did not want to remain silent without reciting anything I said it again for a third time, but now I wonder is my prayer invalid because both times when I recited after the initial mistake were acceptable, so is it like I made a purpose addition in my Salaah or am I excused?

Q: Does repeating Surah Fatiha in the 3rd or 4th rakaat require sajdah sahw according to the other view in the Hanafi madhab that to read Surah Fatiha in the last two rakaats is also Waajib as this is relayed from al Hasan from Abu Hanifa and preferred by Hanafi ulama as Ibn al Humam and al Ayni.

Q: If one mistakenly recites the dua of tashahhud audibly in salaah, is one required to perform Sajdah Sahw?

Q: In order to prevent my cough in Salaah, I halted for the duration of three subhaanallah. Should I make sajdah sahw?

Q: One read more than the half of surah al Fatiha in the 1st rakah, then doubts whether he recited the beginning part correctly. If he re-starts from the place he doubts (and thus repeats a half or more of the whole surah) does he need to do Sajdah Sahw? Thus does repeating a half or more due to a doubt whether one recited correctly or not necessitate sajdah sahw, or does sajdah sahw become waajib only if one forgetfully repeats a half or more?