sajda-e-sahw

Q: When reading in jamaat for zohr, in the second rakaat in tashahud, I accidently start reading the durood thereafter the imaam stands up to read the third rakaat. Am I required to read sajda sahw when the Imam concludes the prayer?

Q: If the Imaam (who is a Hanafi) performed the second sajdah in the 17th para, what should be done?

Q: If a person recites a Surah after Surah faatiha in the last two rakaats of a four rakaat fardh Salaah, will sajdah-e-sahw become waajib?