Sorry to report, but new hubby and I couldn't get certified for OW diving before we left for our HM - we found out right before our cert dives that hubby has a small hairline fracture in his tooth that might cause a lot of discomfort diving.
I do have a little advice from observation tho that I can pass on!
1. No jellyfish! We did a ton of snorkeling and never had a problem. Also, divers we met on the trip reported no stinging things. We did see plenty of sting rays, rockfish, sea urchins and lionfish, all with potentially nasty stingers, so I still wouldn't recommend getting really friendly and interactive with these, but you probably already know this
2. When we still thought we were diving, we investigated the different dive shop and package options. Most dive shops seem to have excellent reputations. We found the best deal (and larger 31' boats for my seasick-prone better half) coincidentally in the same dive shop. Topdive offered us a package of 10 dives (and any additional dive) for about $49/dive, and could be used for any combination of diving in any of the islands on which they have shops, and could be split b/w people. They have shops on Tahiti, Bora, Moorea and Rangiroa, and seemed to be conveniently located are willing to do free hotel pickups.
3. We stayed at the Kia Ora Village hotel on Rangiroa (their sister property the Sauvage across the lagoon is a must do if you want that deserted island with running water experience!). Anyway, their onsite dive shop, the Blue Dolphin, seemed in a bit of a disarray. They had about 13 people in a smaller boat to go out to a dive site, and they couldn't get the dive boat motor to work. Since we have no dive boat experience, I don't know if that was too many ppl, or if this place typically experiences motor problems.
_Bella_:
I was recently in Fiji which is around the same latitude as FP and I could have done with a 5mm. I'm planning a trip to Tonga next July and I was advised to bring a 7mm. Tonga is a little further south than FP. A lot of the diving around Fiji, Tonga and FP are in high current areas where you could benefit from a little more insulation if you have a tendency to get cold. This was a suprise because the operator said the water temperatures were unseasonably warm. I would contact the dive operator you'll be diving with and ask for a recommendation based on current conditions.
(well, that isn't the ONLY one). I snorkeled (only) with my family (hubby is a non-diver "gasp") while in FP. I got cold and ended the snorkel early (just wore bathing suit). Even my always-hot son complained of being cold after about an hour in the water. 
