The basic differences you've discovered are correct. Some more details in the differences are:
Piston actions weigh more than Direct Impingement (DI) or what you refer to as "gas". Technically they are both "gas" operated, just in different ways. The Piston system whether AK or AR (yes, they are available for the AR as well) takes some of the gas produced by the discharge of the round and uses it to drive a piston to cycle the action. With a DI system, the basic premise is the same. Syphoning some of the discharge gas to cycle the action but the gas flows via a tube directly to cycle the action by mating with the Bolt Carrier Group (BCG), also known specifically as the "Stoner Action" named after Mr. Stoner who invented it. So if weight is a significant consideration, a DI system will generally weigh less than a piston system.
As far as the generalities regarding tolerances, the AK is a looser tolerance in general because the parts are stamped rather than machined with a few exceptions (Romanian milled receivers for instance). It also allows for dirt and grit to enter the weapon while it still being able to cycle and function. Still, it has a combat effective range of 350 meters. In general, the AR platform is forged or milled and so the tolerances are machined to tighter specs. Yes that means if fouled by grit and debris it can prevent proper cycling and funtion. It has a combat effective range of 300 meters. Both will do their part if the shooter does his/hers.
As far as brand names go, there are fanboi's for every one. Do your homework and ask around and with ALL the options available these days, you can get whatever you want. If you want to customize it (either one, AK or AR), there are more options available with the AR than there are with the AK.
For maintenance and cleaning, piston actions are easier to clean, but have more parts (inherant with the system). DI requires more effort to clean but has a few less parts to maintain. Virtually even though with the AR you can get a chrome BCG to make cleaning quicker and easier.
If you are a lefty , the AR has options to make it more accomodating where the AK isn't quite so. If you want something a little different you can get side charging upper receivers with your AR (like I did wih mine from ASA). There are ambidextrous charging handles as an option for AK's and there are also vendors that offer ambidextrous controls for AR's as well; i.e. selector lever, EBR's and mag reease buttons.
I can't speak for what is available in Hawaii as far as ammo goes, but on the mainland there is a greater variety in 5.56/.223 ammo in bullet weights, manufacturers, bullet types and prices compared to 7.62. Sight, magazines, barrel lengths and optic options are also of greater variety for the AR's over the AK's. Though time will tell given the growing popularity of the AK's how many more options will become available.
Either will meet AND exceed your present "perceived" needs for the weapon. Price point will depend on a whole different set of variable and I'm not in the islands at the moment so I don't feel terribly qualified to comment other than to say that whichever you choose, you will be happy with. There is plenty of information on both on this and many other gun forums and any or all of your questions can be answered before you buy as well as after.......you just gotta ask.
Oh yeah..........
