i'm a noob to these boards, somewhat new to MMM way of life, but have been living in a rural area of Oahu for 14 yrs. i can speak to some of your concerns here or via PM. i am someone who is not Hawaiian (or any of the other significant racial/ethnic groups here) but i am not caucasian.
public schools across the state are problematic in terms of quality of education and i say that with one kid graduated from the system and one still in it. you should make sure your kid gets into GT/honors/AP classes although i don't think there is GT or any variation of it until middle school. you'll also need to scaffold your kid's education but shouldn't all parents? if your kids need IEPs, i would reconsider moving to Kauai because you may not get the support you need for your child or in the way you want it.
my kids have loved living here. they've run around barefoot, love the beach, hate the cold. my small town has a sort of "it takes a village" philosophy--not on any conscious level but, if my kid dared to do something in the neighborhood that another adult knew i disapproved of, i would know about it before he/she got home.
as for racism issues, those are delicate and can be managed with sensitivity on your part. it is important to understand the history of this place in order to deal with racism here and i say that not as a way to excuse it or condone it but as a way to say that any interaction you might consider racist didn't just happen in a bubble. my husband is white, my children look white and i think i can "pass" but we have not had any problems. we have also not responded to how things are here the way other outsiders have.
i can give you some references about the history of Hawai'i as well as some about Kaua'i and some general keywords to help you look up info. Let me know.