The “Forward Detachment” seems effective as both a tactical formation and a storytelling one. The Soviets (understandably) formalized it to a greater extent, but the basic concept has been used in any army with a fast-moving component. In oversimplified terms, it’s a task force (often a reinforced battalion) used for racing ahead of the main body and seizing/destroying something to aid its advance.
And I think a unit like it is an ideal place to put a protagonist (or antagonist, if the goal is to stop the forward detachment). At least in theory, it solves a lot of issues. It’s small enough that the component characters can be developed without fading in, but is big enough to have a large conventional battle. It can be dramatic and have a clear MacGuffin/goal without sacrificing too much in terms of plausibility.