, two smartphones with chart app and waterproof pouch will get you going, and has many other uses. Keep one below on charge and one in use.
Some form of selfsteering is the best addition to any voyaging boat. A simple QME style windvane
seems to work Ok on the wharrams. It would be pretty high on my list of very useful items. And maybe if the budget
could handle it a electronic tillerpilot.
All this assumes good anchoring gear
and rig and efficent reefing systems. Get the basics right. Sail the boat and add gear
as needed. You can go far with very basic systems and will learn lots by being without all the gadgets many cruisers consider essentail.
All the best, great boats, I sailed a Tanenui in some pretty wild stuff as a kid and was very impressed by its seakeeping and speed.
Oh almost forgot, some sort of drogue
. Maybe an old car tyre or two that can double as a fender
snubber. We nearly had to use it on the Tanenui...
And also a waterproof beanbag, awesomely comfortable at sea and in port.