How many commas can be used in a sentence?
There's no set limit, but it has to make sense, and their use can affect the meaning.
Here are brief explanations of the most relevant comma rules.
You have two options: Oxford comma or no. The Oxford comma is the one that comes before the "and". It's up to the writer whether to use it or not, because its usefulness varies by sentence.
"I love my parents, Lady Gaga and Humpty Dumpty." - Meaning that your parents are Lady Gaga and Humpty Dumpty.
"I love my parents, Lady Gaga, and Humpty Dumpty." -Meaning that you hold affection for your parents and Lady Gaga and Humpty Dumpty.
Two Independent Clauses:
Connect two independent clauses (complete sentences) with a ", FANBOYS ( F or A nd N or B ut O r Y et S o)".
You can connect more than two independent clauses, but that's Dickensian in the worst way, so it's not generally done.
If the sentence starts or ends with a dependent clause or introductory phrase, use it to separate the dependent and the independent clauses.
Surround them with commas. Ex: Freddy, who makes an excellent fruit salad with dates and persimmons, was shot on the schoolhouse lawn.
There are many more comma rules, but most of them are obvious or not commonly used, so I didn't include them all. Check out a full list with examples here: http://www.grammarbook.com/punctuation/commas.asp
Fun Fact: The longest sentence in the English language ends Jonathan Coe's The Rotter's Club, having 13,955 words and taking up 33 pages. Needless to say, there were commas involved.