Your budget isn't unreasonable; however, you may want to prioritize your list between musts (plane tickets for you, your fiance and your parents) and like to have (lots of flowers). For instance, if you choose the right location you may not need so many flowers. Also be ready to DIY for many things (DIY invitations saves hundreds of dollars).
Also WHERE you get married in Kauai may be a huge savings factor. We are planning our wedding/reception in Princeville which makes it very difficult for us to keep to budget; but if you have your wedding/reception in Kapa'a, you have so many choices of wedding locales/reception venues that could save you tons of money. Also your wedding party is small enough that you can order a la carte from a restaurant rather than being forced to do a price fixe menu.
Also you may want to look at hotel/flight packages to reduce costs (I don't know about the States, but in Canada, packaged travel saves hundreds of dollars.) You may want to try a travel agent that specializes in Hawaii travel (e.g., Pleasant Holidays) then do your own research on travel sites to see if they do get you the lowest price.
One thing you shouldn't skimp on is photography. We were depending on having a family member do the photography for us to save money, but a friend suggested having a local photographer who knows the good picture locations, environmental lighting etc. It is an extra $1,500 but for us but it is worth it.
Good luck and keep me posted.