I don't have any special info on Rafts really.  I've tried a few small rafts but never been impressed with them in my big system with a high pH issue.  I also have a couple pipes kinda like NFT but they don't do that great in my high ph system either.  I have not yet really gotten to see how rafts or NFT will do for me if I hook them up on a system with a lower pH.

 

I've been far more successful with media beds and Zipgrow towers.

With mature koi ponds I expect you have a good handle on your bio-filtration but if you want more, gravel beds make for very easy low maint ways to grow veggies and even big plants (banana, papaya.) Over in St Pete, you probably have less freeze damage to the tropicals too.
But since you probably already have good bio-filtration, you could also experiment with alternative growing methods like floating raft, NFT pipes, vertical towers. Kinda depends on if you care how it looks or not.
Gravel beds tend to be more attractive than styrofoam or white plastic gutters all over the place. How much and what kinds of veggies are you going for? Do you want to harvest whole flats of lettuce all at one time (then rafts might be appropriate) or are you looking for family garden plot type variety?

I'm most versed in Gravel beds though I do grow some basil and salad crops in some 4" pipes too. I do have some towers but so far the vertical stuff needs more attention than I tend to give it being as I travel a lot (I don't think I've ever quite mastered the flow rates for the towers.)

The Deck and ponds in your picture there look really cool!