Hi Joel,
Thank you for your questions. Unfortunately, I do not have an answer for these specific questions. I did reach out to my coworker who did the drive from Port Stewart to Coen a few weeks back and he had told me that from memory there were around 4-5 river crossings. It was the dry season when we went up so I have no information on which one is the most significant during the wet season. Nonetheless, I hope this is somewhat helpful.
Kind regards,
Evelyn