Suggestions (please) for an Itinerary for 12 nights in Fiji

My boyfriend and I (in our late 20’s) just booked our flight for a vacation to Fiji in July for 12 nights. We are looking for a mixture of both relaxation and to experience the Fiji culture, and are interested in snorkeling (we do not dive), biking, hiking (seeing waterfalls and rainforests), tennis, laying in hammocks, and possibly other water activities. We could probably spend around US $100-200/night for accommodations, and anything cheaper would be fantastic (although we want our own private room, bathroom and shower).

From reading the posts here on the Fiji branch, there are so many recommended places: (1) the Yasawas (at Oarsman Bay or Octopus Resort); (2) the Mamanuca Islands (but what island is best?); (3) Taveuni; (4) Castaway Island; (5) Nananu-i-Ra (and Rakiraki). With all of these areas and islands within to choose from, I would really love some suggestions on an itinerary. I was thinking maybe going to 3 different areas/islands? Is that too many? not enough?

Thanks in advance for your help!

Taveuni ("garden island") is probably best for hiking/biking (it has rainforest/waterfalls), although the coastal road around viti levu could be cycled. Waya island in the yasawas is good for hiking (octopus and a couple of other resorts are dotted around the coast of this island), but lacks on the jungle/waterfall front as its pretty dry. All 3 different areas is probably a bit ambitious. Maybe try to divide your time between the Yasawas (4-5 nights, relaxation and snorkelling) and Taveuni (hiking and culture). Have a look through lonely planet's guide on fiji, could help you build up a better idea of how to achieve this.

Have fun,
Jamie