The way I read the requirement you have up to 3 days to register with the PD in the county you will be staying in. So if I am only going to be on each island (presumably different counties) for 3 days or less, I imagine I would be ok.
I'm a gun owner in Hawaii. I'm not a lawyer, so ultimately it's your responsibility to write to the Hawaii Attorney General's Office for an official interpretation IN WRITING. If you discharge your firearm you will be arrested based on the interpretation of the local PD, you will be charged or not charge based on the interpretation of the AG, and finally you will be aquitted/convicted based on the judge's interpretation of the law. Usually, all three levels are on the same page but in gray areas of the law you never know.
My understanding is that you only need to register once and don't need to register in all the counties you will be visiting. The first PD firearms office will give you a piece of paper you wil be required to keep with the firearm at all times. It's also my understanding that it doesn't matter how long you stay in Hawaii, you still need to register even if you stay less that 3 days. But you should clarify with AG office.
You didn't mention what kind of handgun you bring...but...just because standard capacity mags are legal in your area, doesn't mean you can bring to Hawaii. If you are caught with a standard cap mag you will be charged with a misdemeanor. If you are caught with a standard cap inserted into a handgun you will be charged with a felony. Don't bring pistol magazines that hold more than 10 rounds to Hawaii.
Use of force:
http://capitol.hawaii.gov/hrscurrent/Vol14_Ch0701-0853/HRS0703/HRS_0703-0304.HTM
5(b)(i) seems to say you have no duty to retreat...but again, get interpretation from AG in writing.
Also, keep in mind, on Oahu(not sure of neighbor island PD policies), Honolulu PD as a matter of policy will arrest you automatically whether the shooting is justified or not. They leave it up to the DA to charge or not charge you with a crime afterwards. You will get arrested, booked and have to make bail. Kind of sucks if you justifiably use force, but in fairness to HPD, even police officers involved in ON DUTY shootings get arrested...only difference is that they are released on their own recognizance while civilians are required to make bail.
No CCW reciprocity w/any state. My understanding is that even non-federal police officers traveling on official business to Hawaii are not allowed to carry firearms.
Anyways, again, get your questions re: Hawaii firearms laws answered IN WRITING by the Hawaii AGs office for the near final word on the law.
Good luck...and hope you never have to discharge your weapon in self defense.
-obm
Hmmm...reading thru 134-3 it seems as though if you bring in a gun from out of state you have to have documentation that you will be hunting or target shooting:
http://www.capitol.hawaii.gov/hrscurrent/Vol03_Ch0121-0200D/HRS0134/HRS_0134-0003.HTM