I've been to Moorea and Bora Bora. At both location, the sharks hang out at the entrances to the lagoons from the ocean. So, snorkeling with them directly from your hotel is not really possible, unless you are REALLY lucky. You really need to take a boat ride to the passes to see the action.
First dive in Moorea, surrounded by 30 - 40 reef sharks. Considering my previous dives were all Carribean, with a lifetime total shark sighting of under a dozen, I was totally in awe. Bora has only one entrance to the lagoon from the ocean, so fewer oportunities for shark dives. But, I think the water was clearer in Bora than in Moorea.
Can't help you with Tahaa or Raiatea..... still on my list of places to visit.
Don't know where you're from, but compared to US prices, you'll find French Polynesia very expensive. Everything is imported, and you're helping to support a very liberal social support system, so expect high prices for most everything. Go for a package deal if possible rather than booking air/hotel/transfers separately. You'll save a bunch that way.