Keep in mind that you are planning to shoot the event in summer — a New Zealand summer! The sun will be high up, possibly hot and no doubt, harsh, unlike winter right now where ideal shooting conditions are everywhere. You'll need lots of experimentation in similar conditions to this, and better still, when it is overcast. Sunset and twilight are ideal but the flash needs to be tempered to avoid the cat-caught-in-the-glare-of-headlights look. One neat trick that many professionals use is a multi-flash: 2 or three very light flashes rapidly, either manually controlled, metered with a flashmeter or taken care of automatically by the flash. It can yield interesting results.