Qiraat

Q: I read Suratul Kawthar reading the letter "th" with a letter "sin" does that break salaah? I read in a fatwa that it does, true or wrong?

Q: In my 'Asr Salaah I recited a verse of Surah Faatihah and whilst reciting I thought I made a mistake, and thought I'd repeat that verse and I didn't
stop reciting until I finished the verse, and then I recited again, but during the verse in which I thought I made a mistake, I was like “Shouldn't I stop?" But I carried on until finishing that verse; now I wonder, does this count as a purpose addition in prayer by finishing the verse in which I thought to have made a mistake? And is my Salaah valid?

Q: First rakat of ishaa I said 'Ar-Rahman Ar-Raheem' but then I don't know whether I said the ha or HA with 'Ar-Raheeem'. I chose to ignore it as a doubt. During Salah I made many mistakes and corrections in the essential aspects - then after completing the prayer [all four rakaats] I ended prayer and did two sujood uh sahw. I went downstairs to get a drink, came back up then I still had the niggling doubt about whether I said ha or HA in 'Ar-Raheem' so I thought like you know it hasn't been a long time since I made Salaam so I said takbir and performed 1 rakaat in replacement of the rakaat in which I doubted with the full tashahhud and exited prayer and did two prostrations of forgetfulness Now plz tell me is my prayer valid or not?

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?