For example were there as many German descendants in the south as there were in the north or as many English descendants in the north as in the south etc? and did this differ particularly state to state?
There's a historian called Grady McWhiney who had a "Celtic Fringe Thesis," claiming most white Southerners had Celtic/Gaelic (Scotland, Ireland) ancestry, and that northerners were more likely to be of English ancestry. He also claimed the southerners were ancestrally warlike as opposed to the English being more mercantile. This theory has been criticized for being inaccurate based on what we know about demographics in different regions, assumes an unbroken cultural continuity between medieval Scotland and 19th century America, and as such it doesn't have wide support. FWIW McWhiney was also a white supremacist and a member of neo-confederate organizations. Also, Appalachian regions with high Scots-Irish ancestry such as West Virginia actively opposed the confederacy, so any ethnic connection between supporting or resisting secession has been debunked.
Criticism of McWhiney can be found here: Walley, Cherilyn A. "Grady McWhiney's 'Antebellum Piney Woods Culture': the Non-Celtic Origins of Greene County, Mississippi." Journal of Mississippi History