Is it permissible for a reciter to recite the Qur’an in the mosque on Friday before the Imam comes out, and is this considered among the Sunnah acts of Friday or among innovations?

There is no evidence for a reciter to recite on Friday before the Imam enters, with people listening to him, and then to fall silent when the Imam enters. The fundamental principle concerning acts of worship is tawqif (to be based on divine text), and the Prophet, peace and blessings be upon him, said: "Whoever performs an action that is not in accordance with our matter will have it rejected."