Method of Salaah

Muqtadi making salaam immediately after the imaam makes salaam

Q: Should a muqtadi make salaam after the Imaam has completed both sides salaam or should he make salaam afer the Imaam turns his head towards the right and then after the Imaam turns his head to left the we follow the Imaam, as we normally do?

Some people in Saudia told me that I should wait until the Imaam is done with salam on both sides then make salaam. Which method is correct?

Obtaining the virtue of reciting Surah Sajdah and Surah Dahr in the Fajr Salaah on a Friday

Q: With regards to Friday Fajr salaah: If I read Surah Sajdah in 2 rakaats one week, and the next week read Surah Dahr in 2 rakaats, will I get the fadheelat of the sunnah? Because the musallees are old, and they do not like to read long salaah. For this reason, can I get the reward for the sunnah?

If there's no sunnah reward for this, then how can I get the sunnah reward?

Muqtadi saying the takbeer when moving to different postures

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?