Getting back to the subjuect of down & side thrust, I think you cannot go wrong by STARTING with what the deigner did.

After that, downthrust is mainly determined by level flight, power on/off, inverted flight, power on/off, and where your CG is for you particular airplane. Very factual.

Side thrust, however, is a bit more loosey-goosey, and sometimes has to do with the pilots preference. Also, the exact body build and where you want to add trim vs let the plane track comes into play.

For example, too much right thrust will not be noticed in level flight, but shows up dramatically in loops. Maybe not even the inside loops, but outside ones. Of course, you have to determine if the variation in looping is side thrust or left/right balance.

I believe it takes at least 100 flights of concentrated effort to really trim out a pattern plane, and even then, you learn a bit more on the second 100 flights, too.