Building optimal RC flying wing I have an EMAX motor that operates at maximum efficiency generating 200g of thurst. This is the only fixed parameter I have.

How do I find the most efficient wing design for this flying wing, considering my motor should push 200g in order to operate on its most efficient range.

I know the bigger the aspect ratio, more efficient the wing will be and more flight time.

I would like to use a KFm airfoil (cause of its simplicity on building it). 

How an RC hobbyst (I am a mechanical engineer too), with not much knowledge on drag, lift coefficients... can come up with an optimal design?

EDIT:

Sorry for being too broad. Let's specify better:

1) my electronics weight (motor, esc, battery, servos...) will be at 50g;

2) I want to use a foam board, typical on rc plane community which is thin and lightweight

3) I want to optimize for flight time, not flight distance.

I am really lost at this, even after searching a lot. I know the vector diagram of my plane (weight is down, lift is up perpendicular to the wing, drag parallel to the wing and I know there are many types of drag but I would assume only the most relevant drag which is the one generated by air deflection and thrust is also parallel to the wing pointing forward).

The only vector that I know how to quantify is thrust and weight. The other 2 I am very lost!

EDITED so it can received answers.
You don't need an optimal design to have fun.  General guidelines:  Your model should weigh around 500 - 700 grams.  Wing span around 1.5 meters.  Chord around 0.2 meters.  But you really need to nail down your speed envelope.  Too fast will be difficult to control, too slow and it's an indoor delight but an outdoor nightmare (due to wind).

A good place to start would be a chunky reliable design similar to a Piper Cub or Cessna 152.  Shorter more highly loaded wings should help you find the sweet spot of around 7 to 25 mph, which is good for R/C planes.

Build an engine/battery/servo frame that can easily change out wings and empennage as you fine tune your design with gliding and powered flights.

You may wish to start with a slightly cambered KFm 1.  Slower speed and lower wing loading should give more endurance, but will be blown around by the wind and will actually be less efficient distance wise into the wind.  Go conservative on your first build.

Control surface dimensions can be had from foamies at your local hobby shop or R/C club, and more information is available at the RC Groups website.