Overglaze Safety
Studio safety is always important when working in ceramics and oil paint. I can't force you to wear a mask and gloves, but overglaze powder is a glaze and can contribute to silicosis, and the pigments can be harsh just like in oil painting. Wear a mask while mixing paint, try to not get it on your hands, try to not get Gamsol/Odourless Mineral Spirits/Turps on your hands if you choose to use them. Don't eat the paint.
But doesn't Overglaze fume? What about lead!
The only fumes that come from china painting are from the fragrant oils that you may use OR typical glaze outgassing. Just like any other kiln situation, you want your kiln to have a ventilation system or sit outside to safely outgas any fumes. No TV room kilns, ever!
Yes, old AND SOME NEW china paints had/have lead in them. Some also had cadmium, selenium, uranium, and even silver. GENERALLY SPEAKING, the lead can't hurt you. You are using so little paint at a time most of the time, and I highly doubt you are eating your paints or glazes. Lead isn't like uranium where if it is near you eventually you'll grow a third toe.
ANY china paint that isn't produced in the USA might have lead or cadmium in it, rules and safety regulations are almost nonexistent to the arts across the pond. New china paints use bismuth based fluxes instead of a leaded flux, so they still aren't great for you. Always exercise caution when buying china paint - if any lead sounds scary to you, there are lead free china paints that do just as well (The Old Ladies might disagree with me there).
I go over more in depth about buying china paints, both new and old, in my supplies buying guide. Check that out!