Below radio info
Definatly do Whangaroa if you have time, and don't worry about a marina unless you need supplies as there are plenty of places to anchor
It's about 20 nm to Whangaroa then another 35 to Keri Keri aprox so it's doable in a little cruiser with a favourable breeze but it will make the trip if you stopover.
You will be in ph range the whole way
CG nowcasting
Location Channel
Doubtless Bay 20
Bay of Islands 21
Or CG on
Whangaroa 84
BOI 86
Far North Radio
VHF Channels: 60 East Coast,
VHF Weather Broadcasts: 0730, 1330, 1730 and 1930 on request