The DLE 20 is a snappy engine in my 60 sized Sig P-51b (search youtube Sig p-51b w/dle 20 for video) but I think would be just addiquate for flying the Four Star 120. I have a kit built Four Star 120 w/ an evolution 26 GT that is good for sport flying but falls short on virtical performance and it has clipped wings (sorry, no video).
For your servo selection go a bit better on the throttle. I used a F3004 on a gasser once... vibration killed it. At least that's what the experts said.
The DLE 20 runns great inverted. See video referenced above keep in mind this was the first flight and running rich. I placed the ignition behind the fire wall. in front of the fuel tank. I guess that could be pretty spectacular should I get a leaky tank stopper or crash just wrong now that I think of it but I did not see an option at the time.
I ran my fuel fill line out of the fire wall and have it flopping in the breeze but a fuel dot right on top and behind the firewall might be sharp looking... unless it leacks on the ignition modual behind the firewall... then we are back to 20 seconds of spectacular.
I would skip the flapperons. The plane is floaty even with clipped wings.
How will it fly with a 16x8? take a video and show us
I think I am using a 17x8 APC with my 26cc and would probably be better with a 16x8. My video referenced above is a MAS 15x8 I changed it to an APC 14x10 and it slowed down and lost virtical performance so I will go back to the 15x8
A .91 four stroke is a replacement for a .60 size 2 stroke. This will not get the 4* 120 off the ground without a strong head wind.
Give us an update as you progress