There is already a post on here that is very insightful and related to my question "go from dev board to production board". However, I need a lower level understanding of schematics. I've searched the web for keywords like migrate hardware from dev board to custom board and how-to reduce dev board footprint to no avail.
I have hobbyist experience in schematics and PCB layout in Eagle and would like to know how circuit designers go about reducing unnecessary components on a dev board like the Nucleo board and its expansion boards to make a tiny custom board. What are the necessary steps required to do that? In other words, how do I know what connections I don't need/need on a 64-pin ARM chip or pins on other ICs? Where to begin with reducing the passive components on the board without disrupting other ICs?
I want to start with DIYing the schematic before thinking about paying someone else to do it. Not sure if this is a doable project for a beginner with minimal electrical knowledge, but input from experienced folks out there is appreciated. I'm eager to learn.