Of course it's OK to PM with more questions - fire away!
Nappies and formula, yep easy as. Which formula do you use at the mo? Callum is on NAN Pro, we used the NAN Pro Gold in NZ with no probs. There's quite a selection in the supermarket although they don't have Heinz or Karicare (which I gather are the popular ones in NZ?).
Food wise, if you're in a hotel jars are probably easiest. They have Heinz here and Gerber and a whole range of good organic ones too, including Only Organic. Fresh tropical fruit is CHEAP too
Nappies - there's Huggies, Pampers, Drypers, Mamy Poko. I think they're the main ones. Huggies are expensive and not as good as the Huggies you buy in NZ but the cheaper nappies are fine IMO.
The weather will be doing what it does all year

Hot, sunny, humid, maybe rainy. You won't need ANY warm clothes, you probably won't wear jeans. Skirts, t-shirts, short sleeved blouses, singlets, shorts, jandals, sandals are all good. Temp ranges from 28 - 33ish year round. It's rainy season at the mo (one big downpour at some point in the day) but should be over by Feb.
Yay. Lucky you getting to come hang out for a week while your DH is working!