1) For the nucleus, we know the relative energy differences between the different levels. We’re dealing with a magnetic hyperfine interaction as this splits the energy levels depending on the z-component of the nuclear spin.
(Interaction with a electric field gradient would split the levels in such a way that the m_I=0 level would have lowest energy.)
2) For an ensemble at low temperature, not many nuclei would be excited into a higher energy level. So most would be in the m_I=+1 state with the corresponding orientation. From the previous video, we know that for an ensemble with most nuclei along the vertical axis where there is no horizontal mirror plane (most nuclei only around positive z-axis) corresponds to polarized orientation (pear-shaped).