Probably not - you're in a very specialist area. I do have books on British Military Longarms, but they tend not to indulge in the details of manufacture. You could look for clues in re-enactors magazines, like Skirmish? Maybe they have the names of gunsmiths who could help you? That's a fairly vague suggestion, but the best I can think of.
At the beginning, not a lot. At the start of the Civil War both sides are depending heavily on muzzle-loading, smooth-bore muskets, and the only real technical advance is the percusiion cap (which makes the musket swifter to load and more reliable in damp weather). So they still blast away at fairly close quarters, depending on volume of fire to compensate for accuracy. But things change. Right from the beginning both sides develop earthworks, field fortifications, to offer their men protection (this was happening by the end of the Napoleonic Wars, but it was more fully developed by the mid 19th century). Then, of course, the rifle quickly takes over from the smooth bore, and once you have a rifle's accuracy then you can't stand in formed units and blast away because you make too easy a target. So the rifle changes everything and forces men to take cover. Technology moves fast - by the end of the war there are breech-loaders and magazines and even machine guns. So at the beginning a Napoleonic general would have recognised the battlefield and understood the tactics, but by the end we're already looking ahead to the carnage of the First World War.
Because all the poor man's promotions are brevet - which is a 'temporary' rank. You could rise to be a general in the army and still only be a lieutenant in your regiment (unlikely, but possible). It's all slightly technical, but brevet rank was frequently used to get round the awkwardness of purchased commissions (if you could only promote officers who paid for it then you'll get a lot of rich senior officers while talented poor ones languish).