Can you provide the names of the books that contain commentaries based on our sampradaya on Shrimad Ramayana, Mahabharata, Shrimad Bhagavatam, Bhagavad Gita, and Divya Prabandham? Can we use the fallen Tualsi leaves from our homegrown Tulasi plant for Thiruvaradhanam? In Shrimad Bhagavatam, Saint Shukha replies to the query by King Parikshit on Rasaleela that we cannot follow the example set by Sri Krishna by citing the drinking of poison by Lord Siva as an example; why would the Saint quote Lord Siva as an example while Perumal Himself had performed countless extraordinary feats. This raises a doubt that a demi-god has been given a hallowed status. Can you please clarify? Can we wear Tulasi garland all the time? While Parasurama is the indirect incarnation of Perumal then how did he not win the battle with Bhisma a mere form of Ashtavasu?

Books on Sri Vishnu Puranam and Mahabharata are published by Sri Narasimha Priya Trust. There is an old edition of Ramayana, shall enquire about its availability and revert. APN swami has published a book on Bhagavad Gita. Divya Prabandham commentaries are based on our sampradayam only and you can buy from wherever they are available.
Fallen Tulasi leaves are not used for Thiruvaradhanam as we have to pluck fresh Tulasi leaves by chanting the relevant mantra.
Saint Shukha has quoted Lord Siva as an example because while we cannot even do the feats of Lord Siva, how can we even attempt the feats of Perumal? He has stated only based on this perspective and those who have written expositions have also stated the same.
Tulasi garlands have to be worn only when we are pure, that is mostly in the daytime; at other times one has to be careful in not acquiring taint to wear it.
Though Parasurama is an indirect incarnation, the Jivatma resides in him; it was the Jivan who lost the battle. Through the power vested by Perumal upon him, he was able to defeat the Kshatriyas whereas the form of God did not fructify while waging battle with Bhisma and he was just a human. The indirect incarnation nature is such that certain actions are based on the power of Perumal and certain other actions pan out similar to normal humans. When the indirect power ends the person becomes ordinary.