Do you need a guide for this trip or can you go by your self?
We used a guide because we have a 3 year old and my wife is pregnant so we wanted someone with us just in case but you can definitely do it alone. Just rent a kayak anywhere at the river entrance or if you don’t want to kayak that much, rent it at the “Hawaiian Village”
I do think you can elect to do your own but I would check with the other companies going and get their trip time. You may find a hole in there where you may practically have the falls be yourself. We spoke to two of the companies and each you had to pickup your kayak and they would give you foam blocks for the roof of your car (ours was a rental with no rack). One thing about a rental is I think you may be able to also go to the fern grotto ( but check the rental company to be sure). Navigation wasn’t that complex but there were portions of the trip we were out of coverage which for some may affect their ability to navigate. Also take into account of course if you have an issue you may be on your own for a bit
Get quick answers from Kayak Wailua staff and past visitors.