1. if the Church Fathers were part of the deception, we'd basically have no Christianity left. These guys literally learned from the apostles or their direct students. Like, Ignatius of Antioch was taught by John himself. Polycarp too. If they got it wrong from day one, then Jesus failed at establishing his Church, which contradicts his promise that "the gates of hell won't prevail against it" (Matthew 16:18).
2. Job 1:6 literally says "Now there was a day when the sons of God came to present themselves before the Lord, and Satan came also among them." That's definitely God's court, and "sons of God" in Hebrew refers to spiritual beings, not humans. Plus, this adversary has power to afflict Job with supernatural disasters - not really something a human enemy could pull off.
3. Jesus talks about Satan as a separate being constantly - "I saw Satan fall like lightning" (Luke 10:18) wasn't him talking about his own desires falling. And when Peter tries to stop him from going to the cross, Jesus says "Get behind me, Satan" - he's not calling Peter his fleshly desire, he's saying Peter is being used by the adversary.
4. In all honesty, I've never heard this argument. I'll have to think about it, and ask for guidence. But Genesis 3 clearly has Adam, Eve, AND the serpent as three separate characters having a conversation. Hard to have Adam talking to Eve while also being the serpent talking to Eve, you know? Plus, Revelation 12:9 straight up identifies "that ancient serpent" as the devil and Satan.
I'm going sleep now, but the Orthodox position is that if we can't trust the earliest Christians who literally knew the apostles, then we can't trust anything about Christianity at all. These weren't random dudes making stuff up - they were martyred for these beliefs they learned directly from Christ's own disciples.