Id split my time north / south in Fakarava. The passes there are awesome but quite different. The South is probably the best in the whole of FP, the North coming pretty close. The pension there is pretty basic, but you are on teh doorstep of fantastic diving, and the locals there have pet napoleon wrasses that will swim up into the shallow to play with you.
At that time of year you might want to head to Rurutu for the Humpback Whales too, you might just catch them.
Mo'orea is great fun, get a car in tahiti and drive over so you can have more freedom. Bora Bora is nice but overpriced, Huahine and Ria'atea are really cool. Ria'atea has some cool stuff to do on land but poor diving. if you want cheap but fun lodging in Mo'orea pm and i'll send you the mail for a cool little surfers place.
Bora Bora is good for the sharkfeed dive and Manta Dive. You can see the lemon sharks at mo'orea too.
In Rangi take a day trip to pink sands beach in the south and blue lagoon in the north (beautiful beaches). Dive both passes if you can, might see some big Hammerheads there if you're lucky, but might be too early in the season. There's a vineyard on Rangi too, makes for an interesting day trip if the boys in the group are getting tired of the beach and feel like getting drunk!
On Tahiti proper there are some good walking trips and it's nice to spend a day travelling around the island at your own pace. Tahiti ITI is cold at night and there's a nice guest house near the top of the mini mountain.
Tikehau has some nice silvertip action, but i think you'd enjoy the diving elsewhere in the Tuamotus more than Tikehau, so it's probably not worth the flight expense or extra no fly time.
Wait until Fakarava or Rangi to buy pearls.