Various masaail of Jamaat Salaah and Imaamat

Q: When reading salaah behind an imam, what does one read in the standing position (does the person following read surah fatiha and a surah)?

Q: When should the muqtadi start to change posture in salat (e.g. from qiyam to sajdah): should he start moving immediately when the imam starts saying "Allahu akbar" or should he wait until the imam has completed saying the whole phrase "Allahu akbar"? Or should he, if he can see the imam, wait until the imam has totally completed his change of posture.

Q: If the Imaam breaks his wudhu during leading prayer, I know he can appoint another to be imaam, but is it also aloud that the jamaat does continue each individually their salaah ? Also, if the imaam is just leading 1 person, what is the situation then?

Q: I went to a musjid late, when asr namaaz was over. However, I noticed a second jamaat taking place in the sehen,so I joined it. I got the last rakaat. So after salaam I completed my 3 rakaats. Now, after a few days, I discovered that the jamaat namaaz which took place was by musaafirs, so they read 2 rakaats, and I completed 3 rakaats, what is the condition of my namaaz? 

Q: It takes our imam a bit long to go into sajdah, standing up from sajdah, etc. So what happens, for example, is that after qaumah, as the Imam goes down into sajdah, he says Allahu Akbar, and we also go into sajdah, but some of us reach sajdah before him. Is his and our salaah valid? Should we request him to rather try and do his postures slightly faster? I think it is because of his weight problem.

Q: Would the muqtadis salaah be invalid if the muqtadi hears the imam say takbeer and goes into sajdah after hearing takbeer but makes it into sajdah slightly before the imam due to imams slow movements. Would the prayer be invalid or maqrooh if this happened?

Q: Would the prayer be invalid if the muqtadi goes into ruku or sajdah say the imam is saying takbeer and moving to ruku or sajdah but the muqtadi makes it to ruku or sajdah before him and the takbeer isnt finished due to the imam saying it so slowly?

Q: While praying Salaah in Jamat (congregation) a person was standing far from the Imam and also there were no speakers. At one point the person thought that Imam Saheb said Allahu Akbar, and so he was going to ruku. As he was doing so he found that the rest of the muqtatis were still standing (the person in concern heard it wrong) so he again stood up. Now my question is that is the Salaah of the person, in concern, valid or should he repeat his Salaah?

Q:

1. If when following the Imaam, the Imaam says allahu akbar to go to sajdah and you say it only when he says it but finished before he did. Is the salaah accepted? An is this for all takbeer and salaam? 
2. If you proceed for sajdah only after the Imaam or same time but you are there before he is. Is the salaah valid?

Q: If a hanafi Imaam recites an Aayat of sajdah (that is according to Imam shaafi'ee Rahimahullah and not according to Imam Abu Hanifah Rahimahullah e.g: The Aayat of sajdah that appears at the end of the 17th juz) in salaah, and he is followed by muqtadis of the different mazhaahib, then what should he do in this situation. If he doesn't make sajdah will their salaah be valid? Is there a solution to this?