When installing aftermarket Sport springs, is it:

[1] A "trial-and-error" ordeal. Meaning, install springs, check wheelwell gap, add/remove pads, repeat?

OR

[2] A "calculated" ordeal. Meaning, based on the stock wheelwell gap, Sport spring data, and type of car one can determine exactly what pad combination(s) to use to achieve the desired wheelwell gap?

I'm curious because I want to give my mechanic the proper pad(s) in advance of the installation of (Eibach Sport) springs and (Koni) shocks. Are the pads inexpensive enough that I just purchase an assortment? What sizes do they typically come and approximate cost? I'm running 215/45ZR-17 tires and have about a 2.5" - 3" gap on the fronts. What is a typical gap; 1" - 1.5"?

Thanks for input!

Brian