I'm assuming you mean MB rather than GB...
Graphic novels? Files in the hundreds of MB are going to be best sideloaded (via USB).
Why not install the Mac version of "Calibre" and convert the epubs to azw3, then sideload?
If you're targeting the Kindle market specifically surely the Kindle Self Publishing route would be best to ensure device compatibility,
https://kdp.amazon.com/en_US/