As sciteach says, CG is King! This is the same for all planes but especially for wings, even two cm's off the correct place can cause you serious problems. A suggestion from me would be that, if the plane flies but feels nose heavy/tail heavy then increase/decrease the reflex. Once you have the CG correct then you can make fine tuned adjustments with reflex (reflex is just putting in permanent up elevator, as wings are draggy and don't have the tail surfaces as such), basically just trim the plane out.
Other than that make sure you use fairly big vert stabs if you are going to fly the plane fast. Wings tend to have a rocking yaw motion at high speeds if the vert stabs cannot compensate enough. This can cause you problems when landing.
Make a build thread when you start, I would love to see how this project develops! Good luck and have fun!