Ahhh, more of my old stamping ground. I know those roads and the territory well, having visited, and at times lived and worked in the area at various times over the years. I hope you don't do it ad just a one day trip; there is far too much to see, do and explore there to just be passing through.
The coastal road from Thames to Coromandel is a magnificent. If it was me I would be loading up a few supplies and heading on up to Fletchers Bay, which includes some 40 km each way of unsealed road. At the end there is a great spot to camp to do a bit of fishing, hiking or and general communing with nature. A few clicks before you can see Auckland from the road over a hill.... drop down and that's it for the mobile phone signal, and I don't think there is even a public phone in the DoC campsite there. Bliss.
Still, it might be better to make a summer trip of that, than now.
Another road you'll be missing is the 309, a mostly gravel road over the ranges from just south of Whitianga to Coromandel, with a few interesting stops along the way. Maybe save that one for a longer trip too.
Whitianga to Kopu is an interesting and varied stretch. A side trip to Hot Water Beach is recommended if the tide is right. Dig your own spa in the sand below the cliff there for rest and a wallow.
The Kopu - Hikuai road is just magnificent....
I'm really looking forward to some photos from this trip.
I had hoped to be back in Aotearoa toward the end of this year, but now I am coming under pressure to stay on at work for another semester. Also coming from the Phuket Cricket Group who are after kicking a bit of life back into junior cricket. The glory seekers who bullied their way to taking over have effectively laid waste to what we achieved.... And now PCG want help to get junior rugby happening too.
So plenty to do on this small island, but the reward is only satisfaction; the pay is pittance.