FWIW - did something similar last November

After 4 fabulous days in Abel Tasman, we drove down the West Coast all the way to Haast Beach before turning inland towards Wanaka.

Although its a bit further south, the drive was spectacular including several worthwhile stops (Pancake Rock, Fox Glacier, Cape Foulwind, cheesy bars in towns that have seen better days, ...)

Wanaka is a fabulous town as well