I would check with the producer. I just finished a book and put 25 pages into each file. Big files, but then my FTP site can handle 500GBs of data and I have fiber optic internet.
Hope this helps.
When I record for GRB&D each page is a separate .wav file that is uploaded. Though when recording you may want to just read until you're done and go back to the single file and lift pages to make into individual files. Every company is different, some have proprietary software that they send you, others just want you to send raw files, some want you to send edited files. Good Luck!