I probably know 80 MERLE HAGGARD songs! And another 80 Frank Sinatras.
You can start out with that many, but as others have said, you must constantly be adding to your repertoire.
Unless of course you are a big star and only need to do a medley of your million-sellers!
Just start with what you have and EVERY time somebody requests a song you don't know, tell them you will learn it and play it the next time. Then do it.
DonM