Could you describe Sai Baba's unusual sleeping arrangement in the Masjid and explain what eventually happened to the plank?

Certainly. Chapter 0 describes a unique sleeping setup. A devotee had given Maharaj a wooden plank to avoid the dusty floor of the dilapidated Masjid. Instead of using it on the ground, Maharaj suspended the plank from the rafters with old rags and slept on it. While on this hanging plank, he would keep four lit lamps at the corners. This peculiar sight attracted many curious onlookers who would gather to watch. Because this became a significant distraction for the people, Maharaj eventually broke the plank to put an end to the spectacle.