RE: Unofficial
the coupler is unnecessary unless you get a boat with a u join as a coupler.
the motors are big, most of us are using 2040 size motors, the one you linked at the top is 2445, which is about the same size but will draw more power making run times shorter.
water pickup is optional, i run mine through the jet drive so as long as there is water moving through the drive, the motor and esc are being cooled
water outlet is unnecessary kinda, just put a hole that the fuel tubing will fit through and feed it out the back