Is it obligatory to perform the post-Isha supererogatory prayer (Sunnah Ratibah) before the Night Vigil Prayer (Witr and Shaf‘)? And is it permissible to commit to only one supererogatory prayer, without the other Sunnah prayers and Ratibah prayers?

The regular Sunnah prayers (Sunan Rawatib) are recommended to be observed due to the great reward they entail. One who intentionally leaves them does not incur sin, but persistently abandoning them is a deficiency in one's religious practice. The 'Isha regular prayer is an independent Sunnah; it is not connected to the Shafa' and Witr prayers or the night vigil (Qiyam al-Layl). It is permissible to perform the night vigil without it, or to delay it.