WRT fins for Futura, you can remove the painting by sanding with 800-1000 grit wet paper.
WRT stock fins, 1 or even 2 is not enough to fully exploit the range of a board. No surprise, I'm using 3-4 fins for each board. The Hypersonic is a very special case because the fin range is extremely wide : from 7 fins, I'm now using only 4 fins of size 26/32/40/55 cm on that board. By comparison with the iSonic 122W75, the fin range is much narrower, even thought both shares ± the same footprint on the water.