"...Thankfully, smaller micron sizes are not as likely as larger mica particles to float in the air for long periods of time and get breathed in...."
That's an incorrect belief. Smaller particles remain airborne for much longer than larger particles. The general rule of thumb I was taught is that if you can see the particle, it's large enough to be relatively safe, assuming the material is inert, not a toxin. A healthy respiratory system can do a decent job of trapping and removing these larger particles. Very small particles around 10 microns and under, however, are nearly invisible. These are the particles that the respiratory system is not efficient at removing.
"...http://www.uline.com/Product/Detail/...dard-Dust-Mask..."
This product is a nuisance dust mask that isn't rated for any kind of serious respiratory protection. For more information about choosing an effective respirator, see posts 12 and 20 in this thread --
http://www.soapmakingforum.com/showthread.php?t=50259.
The other aspect y'all are not talking about is that even if you wear a respirator, at least some of the particles you are concerned about are STILL going to be floating around in the room air after you finish using your powders. It is true that the concentration of particles will be lower due to dilution in the general room air and due to the larger particles settling out, but if you don't want to inhale this stuff at all and you don't want to expose other members of your household to these particulates, then you need to be thinking about using better ventilation to physically remove the particulates from the room air as well as wearing an effective respirator. Or thinking about using the powders outdoors -- that will eliminate the issue of them getting into the room air.