Can I target any number of creatures, even if the ability would have no effect?
No.


  601.2d If the spell requires the player to divide or distribute an effect (such as damage or counters) among one or more targets, the player announces the division. Each of these targets must receive at least one of whatever is being divided.


This is also mentioned in the Gatherer rulings for Aurelia's Fury:


  You announce the value of X and how the damage will be divided as part of casting Aurelia’s Fury. Each chosen target must receive at least 1 damage.