Put gear on, go ride bike?
Around about 1000km to Cape Reinga and back, that's a good 1k to get under your belt. Go round East Cape and back, could be any distance over 1000km, depending on how far south you go before turning around. Coromandel loop is 400km+ from Auckland return. Used to do that at night, leaving Auckland around 10pm - midnight. Capital 1000km Cruise is on later this year, TT2000 next year, and there are a couple of thousand miler events (1600km) each year. However, start by being comfortable with 4-500km days, then builid from there.
Eventually you'll realise our island is a little small tho
Oh, and you're going to rack up expenses. Fuel (duh), tyres, servicing, even turn your gear into consumables as stuff wears out faster when you use it more...
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