Of the nine Union regiments I painted up for my 28mm ACW project, I did one that represented the state I live in and also a unit I reenacted with for a number of years.
Perry plastics are a great way to build Civil War armies of large size at an economical cost. Since the vast majority of Union infantry was based more or less in a generic, standardized uniform with the additions of varying ratios of hats and caps, different colors of canteens/blankets, etc.
So with the Perry box you can build 95% of the Union regiments that existed in the Civil War, with only the addition of particular unit flags added. But even then, for large armies you can get away for the most part with using generic U.S. Volunteers flags for most Union regiments unless you are stopping to paint a specific unit with a distinctive enough set of flags. There are obviously certain state seals on regimental flags that are noticeably distinct in 28mm.
So for my 14th Conn., I got GMB's "Connecticut Volunteers" flags. They are not specifically 14th Conn., but have the correct Connecticut state seal.
Plastic models take Citadel Contrast and Army Painter Speedpaints very well. It seems at times that primed plastics in general take transparencies/inks better than primed metals do. It also depends on what kind of primer you use. I've noticed that certain spray can brands provide a much better finish over others. There is also a noticeable difference in using airbrushed on primers. In some cases models can look a little grainy when you put transparencies over a sprayed primer. Takes some trial and error.
I think this unit came out very well using the Contrasts and Speedpaints.