like other people have said in here, i would say there isn't a true science to finding your "best" setup, other than experimenting and seeing what you like.
i think there is some truth to the idea that your body/shoe size will impact your setup. i have heard of people with big feet (sz 12+) claiming that a 7.75 works best for them, frankly i'd like to see them skate on it. i would expect their skating is probably sloppy and awkward, even by amateur slapper standards.
that being said, maybe your wheelbase at the axles should roughly match your shoulders, but where are we talking about on the shoulders really? shoulder blade to shoulder blade? from end to end? not really a specific science IMO, more a suggestion.
is there really any science to suggest why someone would prefer a shaped board? probably not. you would just have to try it and see if it works for you, for whatever reason.
i found what i liked bit by bit. first i noticed i preferred a deck with some length, by chance. then i went for an 8.5" after the homies laughed at my feet hanging off both ends of an 8". kept sizing up to a 9", realized that was too far, so i compromised with 159's and an ~8.6". i've stuck with 54mm wheels cause that was as big as i could go before ghost pop/wheelbite starts happening. etc.
i think there is some flexibility in what might work for you, which is why so many fools on here end up with madness. for me, i've liked krux and theeve trucks, but stuck with indy out of the slightest preference. deck wheelbase from 14.38 to 14.75 feels nice, with different benefits on either end. i could probably skate any of them and be happy, or keep varying setups and driving myself nuts hunting for "perfection". sticking with something might be part of getting a perfect setup.
fact of the matter is unless youre rich, and have tons of free time, you aren't going to be able to try out every single product variation. you wanna buy every wheel brand out there, and spend a couple weeks on each? have fun. but, you can easily make a note of what you noticed when you tried something different, and apply it next time your current gear wears out.