Yeah, I've never heard of four. Some boards have 3. Two on one end and one on the other. A lot of guys ride with only one fin also. That way they can do a variety of tricks w/o changing their setup. You'll want fins if you're just getting into wakesk8ing or want to go wake to wake. No fins if you want to do kick tricks.
I had an old LF 40" skate and custom drilled holes into each end and installed 4 of the LF cupped fins(2 on each end). I also took off the center fin. It rode pretty well. Really loose, like it was finless, but held into the wake with no problem.