Qiraat in Salaah

Q: After a sajdah Ayat in salaah, does one recite Bismillah before continuing with the qiraat?

Q: I read that in the 3rd and 4th rakaat of qadha salaah (zuhar, asar, maghrib and esha) you can pray subhaanallah three times instead of Surah faatiha and the Salaah will be valid and you will have fulfilled the right of the Salaah. Is this true?

Q: If one has many years of Qadha salah can one read one ayah per rakah, eg. the starting ayaats of Surah Baqarah, is it sufficient to recite 1 ayah which runs into 1 or 1.5 lines?

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

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:

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: 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: Assuming in the first rakaat of witr, one recites Surah Lahab and Surah Ikhlaas in the second rakaat. Is it necessary to make sajda sahu as only Surah Falak or Surah Naas can be recited in the third rakaat but these Surahs are longer than Surah Ikhlaas. Likewise, in any other namaaz, if one recited a Surah in the second rakaat that is slightly or much longer than the surah recited in the first rakaat, what is the ruling?