I wasn't born or raised in Hawaii, but I am on my sixth year being stationed there (okay one was in Afghanistan and now I'm in Iraq...I guess my wife is on her sixth year of being there). Oahu has its distractors and annoying parts (traffic, for example), but beauty and photographic subjects abound. Plenty of plants and leaves, even in the downtown area. My wife is an artist, and I've watched her take countless workshops and classes where an instructor says to meet on some small street downtown. I usually cannot imagine what could be there, but, when she returns, there is always an interesting watercolor or pastel or oil canvas. My usual reaction is to ask for the street name again, so I can make my way there with a MF camera or my Crown Graphic. My usual kit is somewhat similar to yours, and I've carried a Domke bag or messenger bag all over Oahu, always enjoying it. Even after living there for a few years, I always find something else to photograph.
Reference leaves and plants - I absolutely love the trees in Hawaii. I have photographed them on the Big Island, Kauai, Maui, and Oahu. To be honest, my favorites are from Oahu, some as simple as Plumeria blooms off of trees in our backyard, others as complicated as the massive roots of the centuries-old Banyan trees near the Iolani Palace. It is never too hot on Oahu, but the trees in Hawaii provide excellent shade.
There will be a lot of people, no matter when you go. Get a nice rental car, enjoy Hawaiian music while you drive, and look for those trees (and ignore the bad drivers). Walk where you can. I might disagree a little with Mr. Goldfarb above - in my opinion, staying on the North Shore no longer means avoiding the traffic and tourists, especially on the weekends. If the swells are up on the North Shore, add plenty of cars parked on the sides of the one road that runs along the North Shore. Having said that, great ocean and sunset shots, surfer action shots, and more leaves and plants shots are up on the North Shore.
Carry all the film you think you need. It seems fewer and fewer camera stores are in Hawaii. The ones that are there cater to tourists and do not have much more than digital kit, with little, if any, stockage in 120, sheet, or instant pack film. I usually have to order all my film online from B&H and send my Velvia out to A&I Labs, in CA, for development. I do my own B&W, so I'm not sure if anyone is still doing any commercially. My usual experience at Oahu and Maui films stores, before we deployed last November, was that I would ask what 120 film they had, and they would pull some dusty tupperware container out from under the counter and start rummaging through an odd lot assortment of film (my wife always asks afterwards why I even asked, when I knew the answer...). My uncle used to say that everyone needed a hobby, so that they would have something to do when they went to a new place. Don't bother looking for the camera shops, on Oahu.
Take care and enjoy the Hawaiian islands. Best regards, Dan