Q&A for How to Make Garlic Powder

No. Dry the garlic for couple of days in the sunlight, then use the dehydrator for a shorter time.

This will probably make your kitchen smell a bit like garlic for a while, but dehydrators have a reputation of making different areas smell like the food they're dehydrating. You might want to consider using a dehydrator outside if that's an option.

Have a separate grinder for things like garlic or other seasonings. They aren't that expensive. Otherwise you may have to get used to garlicky coffee.

Hardening or clumping is largely caused by moisture/humidity. A small marshmallow in the pot can help keep humidity at bay (works well for sugar, too).