Looking good so far, I like the cannards, they would allow you to change the flow of air over the entire wing, and so give a great deal of control, even in thin atmosphere.
With the tail, how about if you lifted it above the forward wing using some fins mounted on the wing itself? That would leave room for the engine to mounted in the main body of the plane. That way you could make it a rocket plane...
However, if you want to make another turbo jet you will need to find a good way of mounting some extrnal engines.
Heres a prety rough example of what I mean, I think you should keep the overall light-weight look though, this preview is too chunky and blocky;