Various masaail of Jamaat Salaah and Imaamat

Q: If there are a few musjids in an area, which musjid will be the best to perform salaah in? The oldest musjid or the musjid with the most musallis?

Q: Does a muqtadee have to recite the takbeers in salaah when going from one posture to another?

Q: A late comer joins me in salaah while I'm performing my sunnah salaah. Is it permissible for me to change my intention of performing sunnah salaah alone to performing in jamaat?

Q: We have a small musallah in our area. My question is, I am hoping to perform salaah as the imaam with 1, 2 to 4 musallies every day, but most of the time, I'm reading salaah alone as the imaam in front. Will I still get the full reward of salaah with jamaat?

Q: Can you run for salaah if you're late? I have seen prominent people doing this. Not outright running, but a very fast walk that a person will have to run after them if they want to catch up.

Q: There's a few brothers in a masjid who usually don't like when any scholars from different localities come to their masjid, when jamaat comes and even their own Imaams. They find fault in them. For example, they say that one person is reading too fast, another is making ruku and sajdah too long and they only come when the Imaam has to go on the mimbar for the khutbah.

Will their Salaah be accepted like how they don't appreciate their Imaams? Please advise as to what the normal brothers can do and also what the Imaams can do.

Q: Is saying transitional takbeer (Allahu Akbar) when going to ruku, sujood, qiyaam obligatory upon the individual praying behind an imam or can he just follow the imam.

I have performed many prayers behind the imam and I thought I wasn’t obligated to say the takbeer besides takbeer al ihram. Would my previous prayers be invalid otherwise even if I were unaware? 

Q: Due to my slowness in reciting the tasbeeh in the last qadah, the imam almost always makes salam before I can complete my supplication which has to be done after Durood. Please advise what I should do. Please note that the slowness is due to my adherence to tajweed rules in the durood and at-tayiyat.

Q: Is it sunnah or nafil for the imaam to turn his face after saying the salaam of the Asr Salaah. Please explan it.

Q: Regarding the hadith which says that a person who performs salaah for 40 days with the first takbeer will get 2 certificates, is the first takbeer when the imaam starts the salaah or when the imaam goes into ruku?