the black wire lead stays unplugged, you can on a later date add an ignition kill switch (Killer bee) that will connect to the black lead so you can turn it off with your remote (it also act has a failsafe in case of loss of signal, low battery and total battery loss).
to turn off the boat you need to setup your radio the same way you would for an on road vehicle, apply the brake. on your vehicle it would brake, but for your boat it will close the carb.
adjust your throttle so you have a nice idle and adjust your radio so when you hit the brake, you close the carb.
for refueling, the red valve with the white cap is your refueling valve, it is a Dubro Large-Scale Fuel Valve, you need the Fuel Valve Probe to use it, ask the person you got it from if he has it.
here is a link to the Fuel Valve Probe that you need:
http://www3.towerhobbies.com/cgi-bin...?&I=LXD750&P=7
I have been using that valve system for 5 years with zero problem.
Also I would get rid of the champion plug and replace it with an NGK CMR7H. Champions do not like water and are known for breaking and having pieces bouncing around with the piston.
make sure you do a good oil/fuel mix ratio.
your engine being a BH tells me it may be modified however, I suggest that you run no less than 8oz of good oil per gallon.
Don't worry, it is not too much and you will not have any power loss.
Dan.