If it is your first ferry then I would also endorse DeHav's comment, get a pro to organise and go along with you.
Depending on winds and time of year suggest Santa Barbara or Hollister - Hilo - Christmas Island (but check for fuel first) - Pago Pago (Apia also works but fuel can be more expensive) - Nadi - AUS if your destination is not SYD or BNE clearing customs at Lord Howe is real easy.
You can also go Hilo - Majuro or Hilo - Tarawa (check for fuel first). The southern route gives you shorter legs and more divert options.
As for VH vs N rego, I have never had a problem VH, just make sure you have all the paperwork in order. And besides getting as much work done as possible in the US will be cheaper than Australia.