I recently read Civil War Tactics by Earl J. Hess. This book looks at regimental-level tactics and is a real eye-opener for wargamers. We have some conception of different manoeuvres and formations used in battle, but this book goes into detail about how and why each formation was used. How colonels changed their formations in battle, and why drill was important even in the fabled 'Age of the Rifled Musket'. I supplemented this with a pamphlet called Casey's For Reenactors. This translates the contemporary drill manuals into understandable English for a modern audience, with plenty of diagrams.
I want to create a wargame where you are the colonel of a regiment, and you have to give proper orders to your men and lead them in battle. Not just 'move', 'shoot' etc, but give the proper drill commands. Random dice might mean your men bunch up, spread out, drift off centre while marching, or simply not hear your commands.
It's all very embryonic at this stage, but I've gone far enough down the rabbit hole to get some 6mm Baccus ACW models. These are going to be based on a 1:3 scale, so the regiment will be about 100 or so figures.