There are a couple of things I am trying to figure out. Here is goes...
--Would any 8spd derailleur (front or back) work with any 8spd shifter within the same brand? Or are bikes designed to take very specific crankset/derailleur sets? In other words, can I take a crankset off another bike (assuming both are the same speed) and put it on another without replacing the derailleurs?
--If one were to be building a bike from scratch, how would one know what derailleur/crankset combination to go with?
--What are the advantages to different chainring teeth count?