Autocasts should be based off another autocast spell, except arrow spells. They cannot be detected through "Unit Starts the effect of an ability". They are far too tricky to be obtained through basic triggers and make them MUI as well.
Auras, indeed depend on its effect. If they are supposed to give certain bonuses to units affected by aura, then we have a problem. If you just want them to do an effect around the caster to all the allied/enemy units, like healing them every second, or stuff like that, then its very easy. Just pick up every unit with the aura ability, followed with the pick up of every unit around the unit with the aura, and do the effect. Make this a repeating trigger.
~Daelin