I have written most of my own content, but when I need specialized articles [stuff of which I know little ;)] I try to engage freelance writers.
Early on I discovered that freelancers appreciate direction, framework and outlines. They are not able to read my mind, after all. I usually suggest article titles but leave that open to creativity.
Seldom citing a word limit, I usually say, "Tightly written, as long as it needs to be, and not word more."
I usually end up paying $.03 - .05/word. Sometimes when contracting a suite of articles, I will buy a block of words, maybe 5,000. That lets a good writer balance article lengths "as long or short as it needs to be".