Hi,
Hope you are doing well!
Legally you should know following things:
If your annual turnover is greater than Rs. 20 lakhs, then you have to get yourself registered under GST.
Books, generally are not exempted from GST. Specifically, you will have to check notification 2/2017 -CGST rate if the books that you sell are exempted.
Thanks & Regards,
Payal Chhajed