Is it obligatory, recommended, or legislated to send blessings upon the Prophet, may Allah bless him and grant him peace, before seeking forgiveness or supplicating for one who wakes up at night and recites the reported supplication?

Whoever awakes at night and recites the dhikr mentioned in the hadith (definition), then supplicates, his supplication will be answered. And if he performs ablution and prays, his prayer will be accepted. There is no evidence for the desirability of invoking blessings upon the Prophet after this specific supplication, but it is among the reasons for the acceptance of supplications and is desirable before it. Seeking forgiveness and supplicating are encouraged during the time of dawn.