Use a comma before an ampersand or “and” is either a British or an American form of English or both styles.

From the use of singular to plural, both are acceptable under certain circumstances, which you’d even have to provide. E.g.

… on the following Mondays:……

Monday the 4th, 11th, 18th, 25th of January.

How do I find a month and day in my calendar?

The usage you have shown correct, aka “Musica” is incorrect.

Anything parenthetical, i.e.. what is used on a letter? Anything that is optionally dropped, must be surrounded by commas. In this case there will be a comma after the “and” in order to surround “as a result”. British and U.S. comma usage can vary but this is one thing these two cultures are united on.