How close was the Moon to the Earth during it's formation?
We may never know!
Although i have replied we may never know, we may make a hypothesis! This is what most scientists do to make a unified theory about the universe, by assuming variables.
So, when the Earth was made, the moon definitely would have been closer but we do not have strong evidence for it.
The moon today keeps moving farther away from us, hence we can tell that the moon was pretty close.
We can also tell this by the intensity of the tides in the past. If tides had been larger, then the moon could have been closer.