No one is answering barb - so I'll stick my oar in. I have never grown Stevia, so I don't really know how it feels when dried. But for all the other herbs I dry I just rub them between my hands and they crumble easily. I don't think they will need 'pulverising'. I don't see why there would be any safety issues, unless you had hung them to dry in a polluted environment.

Some health food stores used to sell powdered stevia leaves. I still have some from years ago. You just use it to taste for something like tea. It is a little bitter if too much is used and it's best mixed with another sweetener, IMO. The powdered leaves will give whatever you use it in a green tint(so in tea it wouldn't matter). I still use it occasionally if I'm making something with artificial sweetener and I'll combine it with other sweeteners to taste.
I wouldn't rub it between my hands, though, as the sweetness will 'cling' for a while. A mortar and pestle or coffee grinder(or rolling pin and ziplock bag)would work, but let the powder settle before opening a grinder if that is used. HTH

There's a new thread on baking with stevia that just popped up in the cooking forum that you might want to keep an eye on if you need ideas for uses...

Here is a link that might be useful: baking with stevia

I have used homegrown Stevia before and I made "tea" out of the leaves and then used it for sweetening tea. Agreed, it does have a little bitter twang, but home grown is less twang than processed stevia that you buy. The problem with stevia is that it is different potencies from plant to plant, and also, I think, from year to year depending on growing conditions so a lot of using homegrown stevia is trial and error. I would think powdered stevia leaves might not sweeten uniformly but I don't know for sure since I never tried that. Good luck! --Ilene