I use the all up weight. In general the electric power system ( servos, pushrods, control horns, hardware. Motor and mount ESC, connectors and battery pack ) will weigh about what the empty airframe does (+/- 10%). These are ball park rules of thumb I have found to work well for pure bread electric airframes not conversions or one size fits none type of planes (but still good guidelines) So If your empty frame weighs 6oz plan on choosing gear that weighs a total of around 6oz. Note most good gear will have the weight listed in the add. Choosing a lighter weight higher cost ESC so to carry a bigger battery is an example of trade offs. Contrary to popular belief I use an ESC that is rated as close to the max amps the rig will pull. Modern ESC's do fine running at max current all day, just stay within spec. Most now have overload protection so a quick prop strike or even a locked shaft results in the ESC shutting down. So if I have an estimated AUW of 12oz I would be looking for roughly a 25 to 35 g out runner motor. Also note that how an OEM's spec their gear can vary quite a bit between manufactures. Great thing about this level of the hobby most parts are relatively low cost.
By the way that is a great looking plane.