If I were to write a biography of a Sadguru for spiritual practice, does the text suggest a preferred format, such as prose or poetry?

Yes, the Preface provides clear guidance on this. While acknowledging that biographies can be written in prose or poetry, Chapter 0 states that for the specific spiritual practices of study, recitation, Parayan (a complete reading), or Saptah (a weekly reading), "detailed poetic biographies are most suitable." The text further explains that prose is not traditionally used for these devotional readings, in part because "Prose is difficult to memorize," making poetry the more effective and recommended format for such dedicated study and recitation.