Hafa adai and welcome taotaogalu,
I am currently stationed in Guam. I love it here but the local people seem to be hit or miss. But the food and activities make up for it. But yes to crime, especially locals vs US Military personnel. I wanted a CCW for this reason. Most violent crimes are just beatings and theft. Guam isn't big enough to have real gangs and almost everybody is related, so they just have "fight clubs" that troll for trouble in the bars downtown. Stay away from local girls, I know a couple guys that flirted with locals girls only to get beat up! Hopefully that answers the question about violent crime in Guam.
I almost PCSed with all my firearms here but didn't because I didn't. Knowing what I know now it would've been easy. Except I own a dozen and a half guns and to pay a $40 registration fee on each one is ridiculous. The police system is very corrupt here and I wouldn't trust them handling my guns in any way, I've heard some first-hand horror stories about Guam PD.
Anyway, with a box of .223 being $24 out here shooting isn't a popular sport so even if I did bring my guns I would've paid a lot of money to have them here and not shoot them much. I find it odd that you would open carry in Guam, this is a very strange place to do it as firearms are not part of the culture here. Are you LEO by any chance? I wanted to obtain my CCW here as well but the system is so corrupt that unless you are a politician or a big business owner with connections to people in the PD you are not going to get one. MAY-issuse state. Finding a shooting range is a lot of work, one of the only decent ones closed down and the only private rifle range left is on an appointment-basis, you have to call ahead of time so they can have somebody there for you. Real inconvenience.
I have only met one local who owns guns here so it is safe to say gun owners are scarce here. But there is a board at dragguam.com/dragboard where you can buy/sell firearms (if you have a permit) in Guam and meet other owners. I missed a USP 45 for $450 because I didn't bother to get a gun permit in the off-chance that I may find a deal like that. But typically prices are higher. I've seen Colt AR-15s selling for $1500 and a Walther P22 at a gun store for $600.
I think the citizens of Guam should take advantage of the right to own firearms, they still have it easy compared to most countries. I feel the culture just doesn't lend itself to firearm ownership in the first place. No assault weapons ban here so that is good, but no NFA items allowed.
This is what I can tell you about Guam, I cannot speak for the other islands in the Marianas Islands, Micronesia, the FSM, Puerto Rico, or any others.