My impression is that levy would mainly have no armour, not even helmets, Warriors would have helmets and maybe padded armour (like in the WF Saxon fyrd or Viking bondi boxes), and hearth guard would have mail and helmets.
Having said that I've seen warbands where all but the levy have chain mail if the warband is based around one of GBs original plastic boxes of either Vikings or Saxons, and the difference between warriors and hearth guard was shown with either different weapons or different paint jobs.
Whatever works for you as long as you and your opponent can tell the difference.