we have been many places with puddle jumpers to final destination with all of our dive gear. the only penalty is they charge you by the lb or the kg for luggage weight overage. the aircraft we scheduled on from PPT to BOB is an ATR 72, one of the larger turboprobs (68 passengers). for example last trip we flew from PLS to SLX (salt cay, turks and caicos) on a 9 passenger C402 aircraft and had no problems.
we for sure will at least take our snorkle gear, UW cameras, and regs (with dive computers).
Honestly, the overweight fees for the inter island flights in French Polynesia aren't bad at all. You're right, they charge by the kg, and it's pretty inexpensive compared to what fees we see here even just for an extra bag, or now, for the first bag.
We had 8 flights between us, along with both of our dive bags, and the over weight for all 8 flights combined was about $150. We take our stuff, because we prefer to use only our gear but we also go to the atolls and stay over 2 weeks so dive quite a bit.
Bora Bora is nice, not spectacular, not bad, and I think a couple days of 2 dives each will probably get you enough, maybe a third day. That said, I wouldn't be able to go to FP and not dive at all.
We didn't see any shark feeding on any of our dives, and we did see a Manta, quite a bit of coral actually, and black tips of course, and enjoyed it. It's definitely not the same as atoll diving, but we enjoyed it for what it is.
It is easy, relaxing diving, and of the locations you can go in FP, if you are using rental gear on Bora, it should be in really good condition.
Air Tahiti Nui (if you take them and not air france) from LA to Papeete gives you a dive bag for free, if you show your dive card. If you each have a bag, then you each need to show a card. We take our camera gear with us as carry on, and check the dive gear
There's plenty else to do on Bora as well as dive too, the lagoon really is beautiful. ARe you set on the full 10 nights in Bora? Often, people split that 5/5 or something similar and go to two places and an island/atoll split makes for a nice combination. EIther way, have a great time!