When should the one who is praying behind the imam bow? When the imam says takbeer, or straight after the takbeer, or when?

When should the takbeeraat of movement be said during the prayer?

If some of the members of the congregation are praying outside the mosque and the power cuts out

If the imam breaks his wudoo’ or remembers that he broke his wudoo’ whilst praying, it is permissible for him to appoint someone to lead the prayer for him

The electricity cut out during Jumu’ah prayer and they were not able to continue following the imam

Should the person praying behind the imam say Sami’a Allaahu liman hamidah when rising from bowing?

Should he pray behind those who pray Witr with three rak’ahs and two tashahhuds and one salam, and they recite qunoot before bowing?

He was praying a naafil prayer, then some other people prayed behind him, so he changed his intention to make it an obligatory prayer

What is meant by the hadeeth, “Whoever visits a people should not lead them in prayer”

Should he pray behind someone whose ‘aqeedah is not known, whether there are Sufis and Shi’as in the country?