We know deep space stations aren't necessarily in the middle of nowhere as, despite the name, they can in fact orbit planets. K-7 could well have been part of a star system's infrastructure, dependent on regular supply from a nearby colony (Sherman's?) in addition to perhaps helping with managing a number of other colonies at somewhat greater distances. It's not as if DS9 was ever marketed as wholly self-sufficient, either.
As for the yard idea, the storing of the grain aboard K-7 itself remains an oddity. Why would an administrative hub feature grain silos if alternate facilities were available for cargo traffic?