Re: serial comma
Generally, yes. In your example, however, you break up the series with the "as well as." As a result, I would have put an "or" without the preceding comma after the first element.
They can A or B, as well as C or D.
They can A, B, C, or D.
I also personally think that once you have four elements, if each element is longer than a couple words, you should consider whether bullets might make the content easier for the reader.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.