There is no proven evidence which states that a specific number is required for Jumu`ah prayer; for the prayer to be valid, it is sufficient for there to be three or more people.

There is no sunnah prayer before Jumu’ah prayer. When the Prophet (peace and blessings be upon him) prayed Jumu’ah, he would enter his house and pray two Rak’ahs of Sunnah, and he commanded those who had prayed it to pray four rak’ahs afterwards.