For breakfast - yes it is very expensive. I hope it was implied that the $75 rate was for two.
However, you will find that there are many people who report that if you stop at a little grocery store at the beginning of your trip - you can stock up on things like snacks, water, liquor, wine, champage, and beer - and I bet you could get some sort of breakfast items as well. It will save you a ton of $$. We, luckily don't have to worry about the breakfast portion since we're staying at Hilton and have gold status which gets us free breakfast. We are staying at the Hilton Moorea for 5 nights which we paid for in full. Because we got caught right in the middle of Hilton's premium award mess in September, the hotel felt bad for us and gave us an awesome rate of $2700 for 5 nights in an OWB. For the Hilton BBN, we used points and then paid $170 (although the upgrade rate is now $200) per night to upgrade to the deluxe over water bungalow. I have heard that you have a decent chance of getting upgraded to an OWB for free with IC - but you would want to read up on the threads specifically for those resorts for more information.
As far as diving, we are using Top Dive. We bought a 10-dive package in advance and we can split it between the two of us. It was about $1k but we also upgraded one dive for each of us to the shark dive, which was an additional $115 I believe. They also offer free Nitrox if you're certified for it. The package can be used across multiple islands. If you start the package in Moorea it is a little cheaper.
It is recommended that you visit Moorea first, then Bora Bora. Moorea is extremely beautiful, but some people say that it seems less awe inspiring if you visit Bora Bora first - because BB has very dramatic scenery. The big benefit of Moorea is that there are many more activities. It's the only island where you can go horseback riding (I believe). I have also heard that diving is better at Moorea. As far as the more remote islands - they look beautiful and secluded but you will run into trouble if you are looking for activities and variety. Also, on a ten-day trip I would not recommend staying at more than 2 islands (plus the required night in Tahiti). Too much moving around would waste valuable time considering you have to be at the airport a couple hours early and then it takes time to settle into the new resort - thus wasting a half day or more of your precious time in paradise!
The night in Tahiti is only necessary if your flight schedule requires it. If you can get away with not staying there - by all means, do not stay there. A RT cab ride to and from the airport to the hotel will cost you at least $40. However, most of the flight schedules are designed so that you at least have to stay one night either at the beginning or at the end.