If one wanted to learn the details of address space of the ESP, is there any recommended reading material? I wanted to cover that in my book but I'm afraid that I can't find the information I am looking for yet.
this is your normal "address space", I.e. the one seen by CPU
but whatever lives in flash memory is not directly related to CPU address space
some things are loaded from flash into RAM, some things are dynamically mapped at run time, but flash is not a memory-mapped peripheral as a whole
to understand what is loaded from flash to RAM you need to understand the notion of code and data segments. this is not something Esp8266-specific, you can read about data/rodata/bss/text in the context of other CPUs