Early October if it happens, and four nights in Sydney following four in Aukland and four in Fiji.
"And" binds closer than "following", so the sentence parses:
[...]four nights in Sydney following (four in Aukland and four in Fiji).which means the stated (which may be different than intended) itinerary is:
Auckland, then Fiji, then Sydney
And yes, the proposed insertion of a comma doesn't matter.
And why the hell do we even care? Rand has scheduled one helluva trip, I'm envious, and I hope he and the SO have a wonderful time!