How many lbs of chocolate melts will I need for 100 cake pops I am using merckins white 

As much as you will need...

A lot depends on how thick or thin you like your coating... How much waste you create in dripping on the counter... How you may or may not thin out your melts... How big of a container you will be melting them in... etc...

I would suggest purchasing a bit more than you think you will need, but only melt them so much at a time to be sure you aren't burning them or wasting them...