Should the left hand arpeggio be played up or down when there's two half notes in the bottom and a quarter note above?
It should be played upward especially because there are two half notes below with a quarter note above. The half notes are serving a harmonic function here, while the quarter note is part of a "melodic" line running in parallel with the main melody. In general, one plays the "accompaniment" part of a chord before the "melodic" part. This gives emphasis to the melodic line. A downward arpeggio would interrupt that line.