Here is my thought on the CG and stiff "arms" issue - both taken care of at once.
- Use 3 pieces of foam.
1 depron piece. It's the whole top down template.
2 epp pieces. To sandwich the depron, however the epp pieces stop at elevons.
(control surfaces are only depron)
Sandwich the foam with CF rod down "arms".
Cover the "arms" the 'rite way'. Black monokote and riteweave.
This adds weight and strength down the arms.
If not still enough, I use a CF rod to join points of arms at the tips.
EDF. The reason I think EDF is I can have the EDF hang way out in front as the "head" of the plane. This will be a tube but the motor will be in the front of the tube. Also EDF has proper sound. But the motor will be out further then a tractor.
I'm not a builder, I've never built a scratch plane. No experience. However this is something I can mess with and try.

I could always pull the EDF and go tractor at any point... I'll use cheap stuff.