Robert, it's an interesting design you've chosen. Design elements in a semi-scale are almost always compromises. I would not move the engines, or, in the case of electrics, motors, so far apart. Several reasons come to mind, but the main one would be to try to keep the individual thrust lines closer to center so the asymmetrical thrust in an engine out situation is minimised.
I also would try to keep the props closer to a scale location, by not making the nacelles so long. You only need enough legnth to fit a proper sized tank for the engine. Less if you go electric, and mount the battery as far forward as you can in the center fuselage.
The ideal tail moment usually falls in the range of about 1.4 times the wing chord, including the flap chord in that measurement. For example, with a wing with a chord of 10" and a flap chord of 2.5" at the MAC, a good distance, flap hingline to elevator hingeline, of 17.5" might prove to be right. A little adjustment either way can be considered, as it's really a "rule of thumb."
Trying to realistically estimate the final flying weight, will give you an idea of the wing area needed for competitive performance. 12 to 14sq. inches per ounce of weight is a decent wing loading to strive towards.
Once the wing area, and percentage of flap area is decided on, you can figure the size of your stab and elevator. 25% of the wing area, is another good number to consider, but as before, it's all compromises.
Last thing you should really consider is the TLAR (That looks about right) method of design. It's usually correct.