Short answers, pulled from the story.
The Edict of Milan was an agreement reached on the 13th of February 313 AD between Western Roman Emperor Constantine I and Emperor Licinius to treat Christians benevolently within the Roman Empire. The surviving document is not a formal edict but a letter from Licinius to provincial governors, posted at Nicomedia on the 13th of June 313. It granted religious liberty to Christians and to all other religions.
No. The Edict of Milan gave Christianity legal status and ended official persecution but did not make it the state religion. Christianity became the official religion of the Roman Empire in 380 AD with the Edict of Thessalonica, when Nicene Christianity received normative status.
The original letters have never been retrieved. The text survives in two sources: Lactantius's On the Deaths of the Persecutors, which contains a Latin version, and Eusebius of Caesarea's History of the Church, which contains a Greek translation. The two versions diverge in marked ways.
The edict ordered the return of Christian meeting places and other properties confiscated during earlier persecutions. Restitution was to be made without payment or any claim of recompense, and the cost was to be borne by the state, not the current owners of the properties.
Christians refused to swear loyalty oaths directed at the emperor's divinity and declined to pay the Jewish tax, which Rome viewed as a threat to the state cult and to the state itself. Their insistence that their God was the only God could not be accommodated within the Roman system of incorporating multiple religions. Emperor Decius issued edicts against Christians during his reign from 249 to 251, and persecution continued under his successor Valerian.
Historians disagree. The document could be read as a pragmatic political decision to seek the favor of the Christian God and restore social stability. The majority view among historians is that Constantine's adoption of Christianity was genuine, a conclusion supported by the ongoing favors he extended to the Church throughout the rest of his reign.