Something else to consider aka another wrinkle...
Comfort is important whether rowing or using power. You will be sitting there for hours in the boat hopefully catching fish. Will you be rowing a lot e.g. trolling or just moving from place to place for indicator or sight casting for fish? I am fairly tall (6'3") and sitting 8" off the floor is flat out uncomfortable. Leg cramps and back spasms are the norm. Knees in my face is not a good thing! There is no leverage for rowing nor relief for tired muscles.
I addressed this by making a wooden frame that went in front of and in back of the bench seat sitting on the floor with a board over the top connecting them. I screwed/bolted the swivel and seat into the wood to find what was comfortable by cutting the fore and aft 'legs' to the right height (trial and error). I found out the hard way fiberglass and especially plastic was not strong enough to hold the seat. Plus no holes in the boat's original structure! In your case, finding this out, you could make an addition to the top of your bench seat that goes from side to side with additional storage and does not create holes in the original structure. Maybe even add a couple of rod holders and a coffee cup holder? It is even removeable...
Once this is figured out, getting the correct oar length and height is a piece of cake!
Good luck in our endeavors and let us know what your final design culminates in...