I think you might be looking for something like:
${Me.Aura[1].ID}.
This will return 1 if you actually have a personal aura running, NULL if not. ${Me.Aura[2].ID} will return 2 if you have 2 personal auras running, NULL if not (you can have a personal aura and clicky aura going at the same time).
No idea about checking for total castable though, I assume its max 1 clicky + 1 spell per class (2 spells for CLR and ENC)