Nice work !
Happy to see someone interested by this era !
About the artillery, good idea to use Civil war artillery, as Us & Cs artillery were, partly, inspired by french (smoothbore) artillery but if you want to depict the main campaign gun of french artillery (which was a rifled bronze gun - Canon de 4 rayé de campagne modèle 1858) there is some difference in the carriage and you have to add "dolphins" to the gun tube.
Here are some pics (for private use only...)
But you can also depict old 12pdr (the napoleon gun used in civil war arty) which were also rifled, just add dolphins and it will be good !
Here is a photo of a french rifled 12pdr gun captured by prussian and now exposed in Spandau (D) (the carriage is not good)
"Le rudiment", cast in Strasbourg on the 18/12/1856, rifled certainly in 1869...(collection of the DHM Berlin, seen at Spandau)
Enjoy !!
Chris