Use the deflections noted in the manual for low rates. I think that's about +/- 12 on the elevator and about +/- 15 at the ailerons. 20 degrees for the rudder. Check the manual to be sure.

If you're using the 3mm 53 you will not come out tail heavy. The DL is a lighter engine. As usual, don't secure the rudder servo until you know how the plane will balance. The rudder servo can be placed inside the middle of the fue or in the tail just for this reason. It's an easy 2-1/2 ounces you can effectively move from one point to another for c/g purposes.

The ignition and receiver switch locations have an insignificant impact on lateral balance. Unless you're a perfectionist there's not a lot of gain with the worry. If it doesn't consistenly drop the same wing over and over in a hard vertical pull don't bother with lateral balance.

Place the deflection gauge closer to the root of the surface to mitigate the servo twitching if your having any. You're not the first it's happened to during the 5955 set up process and that's how I minimized the issue on mine. Buzzing is very normal for digital servos. They are working against gravity when at neutral.