The Pizazz might surprise you on floats.
I have a Morris "Jerry's Little Boy" that I flew on floats for a coupla' years. It really did not noticeably change flight characteristics between being wheeled and having floats. One of our club members flies several of the Morris profile planes from floats.

I have no experience with the SPAD, but coroplast won't waterlog. I don't know which SPAD variation you have, or how you built it, but you need a rudder (if only an air rudder) to taxi around.

The LT-25 would be fine and relaxing. I have buddies that fly Kadet Seniors that are fully aerobatic, and they still spend most of their time trying for the perfect landing. They have so much fun you have to pry the grin off their face with a crowbar.

There are a lot of misconceptions about floats really dragging down an airplane and that you need a lot more power. This has not been my experience. I know guys who build heavy airplanes whether they have floats or wheels. With a properly sized and correctly installed set of floats, the plane performs pretty much the same as when it was wheeled. Some commercial floats are heavy. I use styrofoam floats sheeted with balsa and they are very light and durable. The floats on the JLB have been on 2 BigLazyBees and a Stick before they were on the JLB, and now they are back on the (Hangar 9 ARF ) Stick. They are getting pretty rugged now, but I have gotten my money's worth.