Module for Winbond W25Q SPI flash memory

the send/write functions can take arrays

Ah okay, that makes sense. So we shall have

• a function to read a chunk
  
• a function to write a chunk
  
• a function to initiate a sequential reading operation
  
• a function to initiate a sequential writing operation
  
• a function to sequentially read / write a byte (optional, since it's just an SPI call)
  
• a function to finish a sequential operation
  
• a function for erasing (less than 16 pages is not possible with the Winbond flash)
  
  

What should the names and signatures of those be?

As I understand it, nothing actually stops you writing the same page twice without erasing - just as long as you don't write 0s over bytes that were already 0?

Correct! I tested this and it works fine. You can see it as writing a part of a page.
(but it should read: "as long as you don't write ones over bits that were already zero")