I fly a Model 4-1200 on 230 lb amphib floats with two people and it works great with the 80hp 912ul. I cheat somewhat by using an IVO inflight adjustable prop, which is a great option on that plane as long as you don't care about LSA. But even without that prop the Model 4 is a very nice, great performing airplane with the 80 hp 912 Rotax. With a 105 hp Zipper kit conversion it becomes a real hotrod. But honestly, the Model 4 with the 912ul 80 hp is a really nice combination. I personally would learn it just the way it is and then enjoy the heck out of it. (You will find it comparable to a 150 hp Supercub, if you've ever had the chance to fly one of those. And as a Speedster, it will cruise faster)

I too would highly recommend going to Paul Ledabrand for training. Don't worry about taking your plane, use the one he has for training. It's a newer model Kitfox, so you'll still learn how to fly a Kitfox. Transitioning to your Model 4 from his new Kitfox will be an easy step to take. Plus you can learn some stol stuff from him while you are there.