I lived on the north shore from '77 to '79 so my info is dated. There are a couple of state parks with camping and trails in the mountains. One is Aiea Heights I think and there are trails out in the leeward side above Mokuliea sp? Above that airfield. ( dillingham?) There's also bound to be a trail guide available......was back then. Even then there were rumors of guys growing the pakololo that didn't like visitors especially haole boys but I think once you get way up on the main ridges you are maybe above that action.
The mountains are really INCREDIBLE. Walking the rim above the Pali and looking down on the windward side is something you won't forget.
My favourite hike was the trails up above Mt.Tantalus above Honolulu. One section went through an old dormant crater. Completely full of massive Norfolk Island Pines and giant bamboo with the totally shaded ground covered in thick emerald moss. Seriously like your imagination of another strange beautiful totally alien planet far far away. Only way you could tell it was crater was walking around the 1/4 mile wide bowl until you realized. It was perched up @ 4000 feet on a ridge. Lots of big eucalyptus too. You keep going up and leave the trees behind and get the "gorse" and then the "krumholz" such as it is in Hawaii. Strange, beautiful, POWERFUL place.
every island has different but equally amazing hiking terrain. Stand on the summit of Haleakala and look down through a big rent in the cloudbank way below at say 5000 feet to the sun dappled ocean 10,000 feet below. It's like you're looking down on earth from another planet. Not many places with a 10,000 verticle view and over on Mauna Kea add almost 5K to that but the angle is longer. Redwoods, Sugi and Douglas fir and Berber sheep on the moors above treeline ( or some kind of BIG sheep with huge racks )and tropical jungle with waterfalls everywhere on the slope of the same mountain