Fiji Aug/Sept

We are looking at Fiji as our first stop on a RTW trip with five children ages 2,7,10,12 and 14. We have both been there before but it was a long time ago. We have a few questions:
1) We were planning to be there starting in mid-August but I have noticed that this is school holiday time in Fiji. How much would this impact budget accomodation and travel? Would it be necessary to book everything in advance? Our preference would be to book the first couple of nights then see what happens from there.
2) When I look at rooms/bures I notice that many are listed as accomodating 6 people. How flexible is this ie- the seventh person is a two year old.
3) At the moment we are not planning to visit the Yasawas or Mamanucas. The resorts look lovely but would be pretty expensive by the time you include transport, accomodation and meal plans for seven. Instead we are looking at the larger islands and would prefer to spend time hiking, swimming and just hanging out rather than organised tour type activities. We hope to mostly use bus and ferry transport with some taxi if needed. We have used both before and are aware of some of the cons (crowding and "flexible" timetables)
4) We will be carrying full camping gear (tents, mats, sleeping bags, cooking utensils) with us for our next destination and were planning to leave it in storage at Nadi. Would it be at all useful to carry any of it with us or will we be fine without? Would camping be an option. I have noticed that it is available at some resorts.
5) Would a three week stay be too long, too short or just right?
Any advice would be very much appreciated.