If they look like ghost crix then your using too much. Its much easier to dust sparingly using a cup and swishing the cricks around with the dust. Using a bag or baggies seems to cause me to over dust also. Just a tip.
Of which include:
3- How many
4- How often
It all has to do with those four factors in my opinion. Veileds and Panthers will allow for more supplementation than a montane species than say, a jackson. Also, a younger speciemen will also need more than an adult. Sometimes, I will feed 10 crickets, and 2/3 will look like little ghost, it is about the equivalent to all of them having a small amount of the supplement of them. Another factor is how often you do it. If you don't do it as often, having a little "extra" than you normally have is acceptable in my opinion.