Oh, I didn’t realize you were dehydrating them! Freezing sounds like a great idea too.
As an aromatic, I’ll throw them in whole (and don’t fish them out since that’s part of the fun :-)). The powder I’ll only add later in cooking.
I first learned to toast them from Barbara Tropp’s Modern art of Chinese Cooking and the practice continues in Fuchsia Dunlop’s books (she says “roasting”) and China the Cookbook. Huang Su-Hei’s books are classics, concise as hell, and introduced me to dishes I didn’t see in restaurants for decades. But they were written for a Taiwanese and international audience in the 80s, when certain ingredients weren’t available, and I’ve found them to cut corners or be seasoned for lower quality ingredients.
According to the article cited below, the heating restriction has recently been removed, but some companies still continue the practice. That said, some of the most potent red and greens I’ve eaten are the ones that pool at the bottom of bags of Huang fei hong peanuts 
