Good time to go Laura, Southern Hemisphere summer, not as hot as Australia, but good chance of good surf the west coast of the northisland is a surf Mecca, from Piha down to New Plymouth, Check our surf map within surfing waves and there are New Zealand surf guide Books.
The Raglan and New Plymouth areas have surf schools and are popular so good chance of company for safety reasons.
South Island different again with an Alpine spine and European cold water, mostly east coast surf especially good, Christchurch to Kaikoura.
Driving back an forth across the alpine spine is scenic but langweilig a bit like between München and Salzkammergut before any motorway.
Great trip though!
I would suggest coming back through Indonesia as middle of 2018 is the swell season for the whole of the Indonesian Archipelago and beginners spots abound, as do beginners.
Are you goofy or natural?
You will find New Zealand unglaublich, enjoy and ask further there are several Kiwi forum members.

I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷