John - It was great meeting you on my last trip to Brisbane........Been to Hawaii 5 times and haven't returned since 2002. Did Maui a lot and it's really just not the same.....Sit in traffic and inch from one stoplight to the next......Can see it all in 2 days and what to do after that? Early April will also be school holiday in the US, so fairly busy.
The Big Island can occupy a week, but doesn't have many nice sandy beaches. Mainly rocky beaches...So bored in Kona, found the only excitement was going to Walmart at midnight. We're talking BORED.
Oahu - can be mass people and traffic jams....Only there 2 days and never went back...
Spent 4 days in Fiji on the way to my last trip to AU.......Loved it and only scratched the surface......Probably like Hawaii was before the 1970's.......That's my recommendation..
You live in kind of a tropical area. You have seen most of Queensland and probably won't find Hawaii much different.....
Romance on Maui:
https://plus.google.com/114816806564667546743/about?gl=us&hl=en
Have fun whatever you do....