Azan Awal Juma

As-salamalikum Ramatullah Wa Barakatuho

I have questions as follows:
Is the First Azan practice as introduced by the Caliph Hazrat Usman (RA) falls under the category of Ijmaa of Sahabah?
Can people just go and remove practices of Ijmaa of Sahabah with out consequences?
Is Ijmaa of Sahaba binding on the Ummah?
OR
Can you please confirm the status of the First Azan introduced by the Caliph Hazrat Usman (RA) and its place in Shari'ah or opinions of four school of thoughts (mazahabs) (with complete references) and which opinion is a stronger opinion?
Is the Salat ul Juma still valid without this First Azan?