"You could go into child key derivation and how the public key of hardened child keys cannot be derived using an xpub. But I guess you are getting there."

Already covered, yet not included as it was still a bit wordy, I'll include it another time.

"My impression is that the G point might have been chosen based on it producing a high enough n before repeating the sequence when adding to itself mod p."

Yes. As for p and n, and don't know exactly, only that that's their denotation.