whenever textbuk.in gets a new customer, Tulpule, who has tied up with Tree Public Foundation, an NGO that works for conservation of trees, plants a sapling at a plantation in Pune. Therefore in my opinion no tax on this business.
Except as provided otherwise in the copyright notification printed in each individual books, renting out of books is legal. The case of Public libraries is always an exception. Public libraries do not rent books for business or profiteering purposes.