Various masaail of Jamaat Salaah and Imaamat

Q: When the Imam says Sami Allah Huli man Hamidah, I try to say Rabbana Wa la kalhamd. But before I finish saying it, the imam says Allah Hu Akbar and goes into sajdah before I have finished saying Rabbana Wa la kalhamd. In this case, should I:

1. Stop saying  Rabbana Wa la kal hamd as soon as the Imaam says the takbir and goes into sajdah?
2. Continue to say Rabbana Wa la kalhamd while following the imam into sajdah?
3. Do not say Rabbana Wa la kalhamd at all knowing that I won't finish it in time before the imam goes into sajdah.

Q: When reading fardh salaah behind an Imam, does one have to read surah fatihah even if the Imam is reading surah fatihah?

Q: If I perform a fard salaat on my own and someone joins in,what is the procedure? My intention was not as an Imam. I am reading silently, do I continue aloud?

Q: After fajr and asar Salah, the Imaam saheb sits facing the muqtadi. Why?

Q: What is the method of making salam behind the Imaam in jamaat?

Q: If person A prays a fard prayer and Person B prays nafl prayer behind him, will Person A obtain the reward for praying in congregation (25/27 times the reward of praying alone), even though the person he is leading is only praying nafl?

Q: Should we recite when Imam is not reciting in namaaz bajamaat?

Q: If I am in Salaah behind an Imaam and my wudhu breaks, do I complete the Salaah and repeat after or do I walk away at the point where my Salaah broke?

Q: Once I was Imam of Esha prayer, my wudhu broke after the second rakat. I did not know what to do, so I completed the namaz. Now what do I do? There were 11 people behind me.

Q: How many men make a jamaat?