When dealing with mysterious elements like whenever God says "Let us", it's important you shelve the information for usage but not fully integrate it into your understanding. These words "let us" used when he made humankind, when he split the people during the construction of Babel, and when he said in Genesis 3: "See he has become like one of us"...

We don't know what us is, and any assertion of the information is wrong, so we're reduced to guesswork. When reduced to guesswork, we cannot solidly take a literal or figurative stance, but need to have both options open for the sake of accuracy.

Some of the information gets exacted later, some of it stays mysterious. For example, Peter talks about God temporally in 2 Peter 3. Time is a tool of reality and something of an illusion while God dwells above reality, so the concept of a "day" is far different to him than our understanding of it. This can open up as many mysteries as it exacts.

Some guesses are: Genesis 1: he says "let the earth, let the earth, let the earth" and then when it came to humans "let us", which could mean God + Earth. (Father + Mother - the father ends up in Adam and the Mother ends up in Eve, the serpent coaxes the object of the mother and tarnishes the creation of the father.)

Some say it's the hypostatic union of the trinity. "In the beginning, the Word was with God".

Some might say he's talking to the other luminaries/angels. And if this is true, then it's possible that all the other angels made all of the other major religions possible, because as Jesus says in John 4: "One sows, another reaps", which means Jesus has come to reap what the other angels have sown.

It's also said in Genesis that the giants were considered the "gods of old": did the Giants and Nephilim also "know good and evil"? Why are men "like gods"?

Whatever the case is, it's most appropriate to leave it in a state of flux, mystery and uncertainty so that you can test more possibilities.

Keep also in mind that God's rhetoric adjusts when the human understanding changes. It's like when a child is two, we treat that child differently than when the child is six because the child is open to new rhetorical possibilities. God's knowledge of rhetoric is also supreme, so he's not going to limit himself for the sake of consistency when we invent that he must be consistent.