It occurred to me that there is a very successful series of mystery stories that could serve as a model, of sorts, for this series: Nero Wolfe.
The stories concern a genius detective who never leaves his townhouse to actually investigate crime: Nero Wolfe himself. All the actual legwork is done by his assistant, Archie Goodwin, who narrates the stories.
The Lecter/Graham team could be a twisted version of the Wolfe/Goodwin pairing. If they mashed this up with Dexter, a season would involve Graham investigating a single case, while Lecter both assists him, plays mind games with him, and pursues his own avocation as a serial killer and cannibal. The final season would portray the endgame in this relationship, in which Graham investigates Lecter himself, without realizing it.