I suggest you ride a knobby tired trike before you decide if the noise isn't that bad. When I finally got off the pavement and on grass with my tad pole, it was like heaven that the noise stopped. I ride for relaxation, not to hear an endless rumble.I worked in Coral Springs for 11 years - it had levees built around it with giant drainage pumps so when it rained more than 2 or 3 inches, the giant pumps would kick on. So, right, you're not too far off with the sea level thing.
On the other hand there are some good sized inclines coming out of bike/golf cart under and over passes. And central FL has some nice hills - not like western NC mountains where I live now, though.
As I suggested earlier, the noise of the tires on a bike is not all bad - a bit of a "here I come" noise will give folks a heads up.
My limited experience with delta trikes generally is if the driver is too aggressive in turns, he will either 2-wheel it or dump over. There is a "leaning" curve (pun intended) involved in aggressive turn management. I learned that when test driving a relatively low slung pedal powered delta a couple years ago.
So which trike do you suggest as a fun hauler?
I have very few places I can go to haul things. I'm very fearful of getting hit from behind on streets from distracted drivers. My wife was rear ended twice in 1 1/2 years in our car. Both times sitting still at a red light! I'm also not a fan of riding around 10mph with a traditional trike. The only hauler I would be interested in is a cargo two wheeler.