hey,i´m here,to illuminate you all with my knowledge about bicycle technics,because thats what my apprenticeship was aiming for,to get me having a clue .
youre both right in your own way,in much cases experience lets you open the drawer with the right spokes without even thinking about it,in others you only get the perfect result only by going the way step-by-step,measure and calculate everything(and i learned to do it by amathematical formula).
the difference for me,in my job,as my profession is that one way is going to just "work out as...",where the other "is.." the (more or less)desired result.
i think its kind of a mindset you have to have when doing it professionally,but you can get a good "private result",too,its just not perfect.
dont confuse wheelbuilding with building a wheel,people which do it professionally will get what i mean with that
edit:and reusing spokes just to get away cheap will only lead you to lacing it again in my experience