When beginning a sentence withso(or any other conjunction), most grammar resources state that you don’t need to put a comma afterso. However, ifsois followed by an interrupting phrase, it would be followed by one of the two commas used to set the phrase apart from the main sentence. ...
so), also known as the aforementioned “FANBOYS.” These connectors join two independent clauses, which are complete sentences with a subject and verb and any additional parts needed to stand alone and make sense. When done correctly, it creates a compound sentence. ...