Here are a few thoughts based on my one and only time hunting the big island several years ago:
Although there is a lot of public land on the big island, unless things have changed in the last few years, there are only a few of those areas that are open to turkey hunting. Most of the public areas do not allow turkey hunting. You would be wise to thoroughly research the turkey hunting there to make sure you understand where those areas are and the rules and regulations that apply to them.
Unless they have clarified the licensing requirements and perhaps changed things, be aware that you will have to go to one (of only two...one in Hilo and one in Waimea) of the wildlife department offices to obtain carcass tags prior to hunting...and those offices have limited hours. You can buy your general hunting license online, I believe, but you have to go to one of the offices to buy carcass tags. Again, this is the way things were several years ago...not certain if they may have changed things at this point.
There are also some pretty strict regulations regarding firearms and the need to register them "in person" prior to hunting. Research that as well.
A final recommendation: make sure you get a rental vehicle that has high clearance, preferably four-wheel-drive, and has a good spare tire. Getting around in that lava-invested country can get pretty ugly at times.
Again, do your due diligence in researching hunting there. They don't go out of their way to make things clear, or easy, for hunters.
