Almost there, but not quite. That approach may work for a DC single cut, or a design where the binding can vary in height, but it aint going to cut it on a LP. If you look at you final drawing, the fretboard would be sitting below the binding, well into the mahogany below.
You first step is correct, but the next step is to calculate neck angle. You consider the top of the binding to be the 'face' of the guitar, and consider the thickness of the carve as part of your bridge, so the bridge height you use is bridge + carvetop - fretboard thickness. Mark this on you drawing, then draw a straight line connecting the top of the binding to the bridge height mark. This is you neck angle. Then, it's as simple as plaing a straight surface bewteen the bridge and the end of the fretboard.