Hey groundshark, (whoa! lots of responses while I was typing...)
I made the same move 7 years ago. Only had a Ruger Old Army that I inherited from my dad at that point so I didn't have to fuss with any of the laws. I have since.

The only magazine limit applies to magazine that ~can~ be inserted into a pistol. That means your 9mm and, unfortunately, any ARs since a pistol version is made. The AR magazine limit is NOT currently enforced, though. Still, I wouldn't waltz into the police station to register it with a 30 rounder. When I register I don't bring any mags at all - not required and visibly safer. If you are in doubt about any of your mags the safest thing to do is disassemble them. Having the parts for 11+ mags is not illegal.
Bullet buttons are NOT required here, thank heavens. You can replace those atrocities with standard mag releases when you get here.
Also make sure your 9mm doesn't meet the state's idiot definition of "Assault Pistol." You're probably fine, as long as its not a semi-auto version of an Uzi. Anything like a Beretta or Browning Hi-Power is good.
Best way to get your firearms here is probably in your airplane luggage when you fly over yourself. Just book your ticket with an airline that allows this. The TSA allows it but the airlines have their own policies. I forget the rules but the airlines post them on their websites. Otherwise you're looking at shipping it to yourself and possibly having to deal with FFLs. If you are shipping other things like furniture and whatnot by boat I think you can include the firearms there. Not sure about ammo. I know small amounts can be packed in your luggage if you are transporting firearms but weight quickly becomes and issue and if you've got a couple battle packs...
Which island?

Everyone has their own opinion, really. Each island is very different.
Oahu is by FAR the most populated with all the pros and cons that comes along with that. The most work, the most crime, the most shopping, the most traffic, etc. Oahu has the best selection of... well, everything including gun shops.
The Big Island, where I live, is probably the most gun friendly due to the relatively high population of local hunters. Pig hunters. We have precious few places to shoot, though. Its a difficult place to move to unless you have family or friends here. Work is very hard to come by and the areas that are more welcoming to newcomers have other drawbacks - crime, drugs, etc. Not more so than Oahu, though.
Maui is... interesting. Somewhat more welcoming than the Big Island and has a hunting culture (including Axis Deer and Mouflon) but it is expensive. And think Country Club when I say "hunting culture," though there certainly are local hunters. The island is generally more welcoming if you have a bit of cash on hand. And then there are the locals and recent transplants who don't have much cash that resent everyone who does. (Can you tell I'm not a huge Maui fan?) Still, it does have some rural left and it is a gorgeous island. If you can find work there then it would be worth considering.
Kauai is kinda like a little Maui that never quite reached a critical mass of cash so the difference between the have's and have-not's is much less. They still tend to feel the same way about each other, though, so its a hard place to fit in as a newcomer unless you are clearly one or the other.
If you have no connections here then Oahu is almost definitely your best choice. If you have connections for work then where ever that leads you is your best choice.
I believe all NFA items are illegal here but I know that silencers and full auto anything are verboten.
Registering is easy here on the BI - either Hilo or Kona station. I rarely have to wait more than 15 minutes. All Arlene does is measure the barrel and check the serial number. Easy. I've heard of longer lines and sometimes impolite officers on Oahu but that's only hearsay for me.
edit: I realized that I'm saying some unkind things about some of the neighbor islands. I mean that from the perspective of what a newcomer has access to. We all know that newcomers don't always have access to everything. Just like any small town kind of place, really. That takes more time.