Was that Seward? Most of it sounds more like Stanton's department.
Not really. First, Lincoln had the corrupt and incompetent Simon Cameron as his initial SecWar. By the time Stanton got in and proved himself both (very) competent and trustworthy, Seward had been doing the work for quite awhile, and Lincoln had become comfortable with him. Besides, Lincoln & Seward as well as Lincoln & Stanton were both very good team ups. No reason to mess with a working formula.
Lincoln didn't like the idea of the stern SecWar exercising military authority over legal matters like the suspension of
habeus corpus, monitoring ballot boxes to prevent thuggery, and arresting large numbers of civilians without charge. While
troops might be employed to do so, Lincoln seemed to prefer having the senior member of the cabinet, the former governor of New York (largest state at the time), taking such executive actions over the more intemperate Stanton, who'd never held elective office and whose only real political experience was serving briefly as Buchanan's AG.
Also, as SecState in a Civil War for survival, there was little to do for Seward beyond preventing foreign intervention. Lincoln simply employed Seward's excess skills diligently.