Well I can tell you for sure Plato was not a Gnostic. Plato did not talk a lot about religion and we know he was a dualist. The only thing he really had to say about religion was that any story, as told by Hesiod and Homer and the other poets, which gives a bad image of the nature of the gods, portraying them as petty, devious, or warring and plotting and fighting against each other.
The Gods, in Plato's eyes, should only be represented as good, and pious, because it is the nature of divinity to be good (which is what we call universal truth). Plato tells us how he thinks the universe was created, but he warns us that his story is just a tale, because we being mortals could never understand, which is true till this day, we have theories but we don't know for sure. He says that the creator, created the universe from his likeness, out of the preexisting chaos, this is different from the Christian view that God created the universe out of void.