"suspension" Is a little vague i guess,.. but to be accurrate suspension is a part of a bigger picture, rather than the other way around.
I believe also that,... you are close but still off the mark when saying that "springs are the number one thing"
I'll state this differently for all,... Not matter what the spring rate is,... (proper rate and sag is very subjective)
If the basic geometry of the bike is wrong for a rider,.. the springs will be at best a band-aid on a problem and could in fact even be a problem,..
Number 1 on anyones set up should be a well recorded geometry baseline,... keeping in mind that factors can and will change this such as changing tires, tire pressure, spring rates preload and live loads ( riders and gas weights).
the best method is to start with basic geometry and establish the best combination of spring rate and preload and dampening to match. not the other way around