Reddit mentions of The Wisdom of the Knowing Ones: Gnosticism: The Key to Esoteric Christianity

Yes, insofar as you're referring to only some of the more extreme dualistic Gnostics, a term given to them not by themselves, but as a sarcastic put down by their opponents - like a "know it all". I forget the ancient greek word that they used to call themselves, but it meant "those who are aimed", their aim being the escape from the material world, as fashioned and governed by the demiurge and his archons, of birth and death, much like the karmic wheel of Buddhism and Hinduism. There's an interesting book The Wisdom of the Knowing Ones: Gnosticism: The Key to Esoteric Christianity, by Manly P. Hall where he writes that much of the ancient Gnostic influence is on account of the inflow of ideas from the east, including Buddhism and Hinduism, as there was a trade rout open to China by 200B.C..

I'm no expert, but I have studied these matters to some degree and they are a fascination of mine, what I can say is that it looks as though there was much diversity in how the Gnostics considered the demiurge's relationship to the cosmos. Some said he is evil as is his material world, others that he's as benevolent as possible and the cosmos as good as possible, only he's ignorant of his higher, divine origins and our cosmos is fallen due to this ignorance and divine mishap.

Yes, Yeshuwa is a manifestation of the Gnostic godhead, to save the lost divine sparks from human souls and even, according to some Gnostics, the demiurge himself.

This is where it gets tricky, Satan, say as the serpent in the garden, is seen to be as the redeemer, but they saw the serpent as Christ - even Moses lifted the bronze serpent to heal the wondering Israelites in the desert, as foreshadowing of Christ on the cross.