Fiji - hints for diving and relaxing

My wife and I are planning a 10 day trip to Fiji and we're trying split our time between diving and relaxing. We've heard great things about Taveuni, particularly the diving, but it seems a long way off from the main island. Are there good dives sites on the main island or should we be definitely be going to Taveuni? Kadavu looks beautiful as well, also with great diving. We both have a couple of dozen dives under out belt and AOW certification.

I'd heard that the only way to get to these islands is by air, are there reliable ferry options instead? We're quite happy to spend time in cheaper accommodations if they're clean, we both done plenty of travelling and can handle the low cost end of town. Does anyone have any recommendations for places to stay in Taveuni, Kadavu or the Coral Coast of the main island?

It is easier to get to the islands off Nadi like the Mamanuca's and Yasawa's most of which have good diving.
Taveuni is a lot harder to get to and it rained every day we were there.
Coral coast is easy to get to but generally not as good for diving as the smaller islands.
Both the Mamanuca's and Yasawa's are accessible by boat.
Yasawa's have more backpacker style accommodation then Mamanuca's.

You could also check out Beqa Island near Pacific Harbor - there is a wide range of accommodations from homestays to resorts. Another area to consider is Nananu-I-Ra Island near Raki Raki - You can stay on the mainland(check out Volivoli or Wananavu resorts) or on the island itself.