Those instructions are for a Honda, not an FFR build.
First, the starter solenoid "S" terminal never draws 30AMPS. I'd say 3 amps at the most for Pete's sake. After all, the starter Solenoid is a RELAY, ain't it?
Next, he recommends 18-gauge wire to hook up the switch. That's good enough for 15AMPS in short runs. There's no talk of a fuse either.
Just to make sure, I would check the current draw on my "S" line and then compare it to the S2000 switch. I'm certain that switch's got to have at least a 10AMP rating.
Way too much overkill for something so bloody simple. I'd just hook up my "S" line to the OUTPUT line of that switch and call it a day.