Re: How to choose string gagues
You can scientifically determine how to balance string tension but there's no science behind balanced tension being preferable. I've been using custom gauge strings for about 5-6 years now and I'll tell you that they're nowhere near balanced in tension. They are, however, optimized for my fingers and ears.
I understand the desire to quantify playability but I also personally decided that it's pointless, particularly so in this case. The typical reason for collecting metrics is to allow for greater repeatability. Thing is that estimating the tension isn't exact (varies based on string materials/construction) and what's most repeatable is string gauge, not tension. When going from one guitar to another (e.g., 6 in line vs 3+3), you might think that you can calculate the optimal set but there are other factors (neck carve, hardtail vs. trem, fret size) besides tension that will affect the feel. Sure, it'll give you a "better" starting point but when you get down to it, preferred tension is a means, not an end, to playability.
TL;DR -- The only numbers worth optimizing are the ones that please your fingers and ears. I'd suggest that you're better off systematically analyzing the qualitative factors that impact playability for you than trying to calculate/measure everything.