The mildest I have is the heat of a habanero, and then they go up from there. Fresh, or still good is two different things. After about 3 to 6 months I notice an obvious degrade in freshness, but most don't have a real big change in taste even after a year. The yellows will actually get off color after a few months, even though the taste may be fine, but the reds keep their color well and seem to hold up better. I'm using regular ghost powder that is 1 1/2 years old and for my purposes, it is fine. When I can, I keep powder made from August picked peppers because it is the hottest, so I'll normally keep that as my own stash for an entire year.
If you really want fresh powder, you keep the dried peppers in a proper storage container and grind them up as needed. It does make an obvious difference if you are picky cook kind of person that always uses fresh herbs when they cook and that kind of thing. I'm not all that picky.