Perhaps something to keep in mind would be to make future garments with a good pattern but to also have something dead-nuts on, i.e. a Richmond Depot overshirt or the like, to reference for future sewing projects. This would be especially helpful to those new to sewing their own period clothing. Unless instructions that come with patterns are so painfully detailed as to make having a properly assembled garment on hand to look at unecessary, getting an item or two made by h-core authentic suppliers is not a bad idear.
The only supplier I know of that would make having a reference piece a non-starter is W., W., & Co/Dan Wambaugh. I put together a Fed SA trouser kit (original SA trousers were 100% hand-sewn) from Dan and was very pleased with his assembly instructions. The many photographs he included detailing each step of the construction process were so friggin' good I didn't need to reference a properly assembled piece to know I got it right. However, this is likely the exception and not the rule at least for ACW military stuff.
Brass