Assuming one uses the serial comma, should there be one before "or"?
The company can create branches in Switzerland and abroad, acquire stakes in other companies, as well as acquire other companies or sell acquisitions.
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.