I did not go far beyond getting the commercial SES. Got checked out in a spam can I could rent, and then never did that LOL. We did the river thing in the Snoqualmie River here.I've been flying float planes since my teens, up to and including some logged time in CG UF/SA-16 and even Navy P5Ms. Worked for Gopher Aviation in MN one summer, hauling MN fishermen, and rebuilt three tornado damaged Cessnas to fund college. We'd often land and take off on grass next to runway on morning dew.
Two Ercoupe negative issues I could see are unsticking if no wind, two people, and more than a shaving kit, AND the linked rudder/aileron with a cross-wind landing/TO. A plus though is it has a low wing that helps with ground effect, while most float birds are high wing.
I got rated in an 85 hp rag wing, no flap Cessna 120 flying off a wide spot in the TX Colorado River on the edge of Austin ... sure was glad it didn't have the 75hp mill.
I liked float flying but I had no friends with float planes, and when renting one cost more than operating the 310 ( at that time ) you know which one got picked.
Down at Cottage Grove Oregon we would stop in for gas and that burger on the way to California, and those guys would slide a float plane in on the wet grass, and also launch one with one of those dollies. I watched that once. OMG that thing did not behave well after the plane lifted off it. It hooked up and cartwheeled. I do not think that was the plan.
There is a nearby river they would tie up at for the summer.