Names Of God And The Prophet (sws)

Could you please share your understanding of the following:-

In salah we recite thanā (a formula said after the first takbīr). What is its source? Is it a part of the Qur'an or a separate wahi (revelation)?

b. What is the source of the names of Almighty Allah and names of Prophet Muhammad (sws)? Is "Ya Jamilo" the name of Allah?

C. What is the source of six "Kalimas" that are taught to every Muslim. Are they part of wahi?

d. I believe that during the time of the Prophet Muhammad (sws) mosque is not only used for offering ritual prayers but also as a place for conducting state affairs and shelter for the travelers and alike. Could such a practice be implemented today to help our rulers aligned with the truth?
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