First of all sorry about my english, second you will need a much simpler project to start, make to work a closed loop stepper controller needs much more that "learn electronics", needs power control (drivers), math (pid?),hardware (encoder mount) so any part may become a problem in the learnnig
A few years ago (well about 12 ears ago
, i have 29 years old now
) i do my start with electronics using a microcontroller that a friend gives to me, i made my own microcontroller programmer with 2 transistors and a few resistors, a multimeter and my old pc with the basic that comes in the DOS, i made the program for the programer (a lot of in and out instructions ) and my first "firmware" a led that blink if one input was high. I worked about a month later but at the end the circuit works. the only tool that I had liked to have is an oscilloscope.
I hope that my point is understood , if you want to lear how to make a complex microcontroller system first you need to know how make a simpler microcontroller project, and normally the difficult part is to know how to make it works and no how to make it.
At my oppininon the PIC is the best to learn becouse this micros has well writen datasheets, a lots of sites whit projects and a lot of good C compilers (i use the CCsc PICC)
Best luck