First off, welcome to the Do-It forums. Lots of intense knowledge here for you to gather in all aspects of tackle making.
The glitter sold at Do-It and a couple other places is designed specifically for the high heat required in plastic making and won't melt regardless of size. The very least size I would consider in small baits is .015 except in black glitter. Any bait as large or larger than a 2 1/2" small fry I'd be hauling out the .040 glitters unless you are mixing the red to be very transparent or thin.
