you only %leech from physical damage (unless you have some SU that allows certain spells to leech) . if your physical damage is converted to another element, you only leech from the part that is not converted . Also , you need good attack rating to get LoA and MoA back from each attack . the %leech suffers penalties as you are changing difficulties and looses it's effectiveness , so you need more physical damage and %leech for it to be reliable in Hell
MO your rings and amulet with %mana regen . that will also help . dumping some points into energy to increase the mana pool a bit would also help . since you are going for elemental damage , that would also boost your elemental procs and the initial melee hit if you carry any elemental damage to weapon