Qiraat

Q: When one recites Surah Naas in the first rakaat, what should he recite in the second rakaat?

Q: My local imam makes some mistakes sometimes in salaah and I need to know whether these mistakes invalidate the prayer.

Mistake 1) The imam sometimes says hamza/alif Instead of saying ein for reciting quran, does this invalidate the prayer?

Mistake 2) For the name of Allah, Al-Quddus in the quran, the imam changes the seen into a saad-does this invalidate the prayer?

Q: What is the ruling on reciting inaudibly, is there a consensus on its permissibility? Like without noise and just moving the tongue.

Q: Why are zohr and asr called sirri salaahs and the Imam would not recite loudly? Any significance? Please explain.

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

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: 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:

1. Can I say Ameen feebly (not bil jahar) or is it compulsory as I live in a Hambli environment?
2. Is doing of rafa ul yadain compulsory? Can one leave it curtesy living in Hambli environment?

Q: When I perform Salaah alone, should I recite Bismillahir Rahmanir Raheem before Surah Fatiha in every rakaat of Salaah? Also, should I recite Bismillahir Rahmanir Raheem after saying Aameen and before I start another Surah?

Q: If in "Ihdeenas-Siratal-Mustaqeem", I recited dee with a daad mistakenly instead of daal does this invalidate the namaz? I don't know for sure if I done it, but it seems likely so should I repeat the namaz or is it an acceptable mistake? I didn't repeat it afterwards.