Judging the size of the pot from the photo, I'd say 3 or 4, depending on the size of the plants you'll find.
But it all depends on the actual sizes! Put as many as feels right when you have everything in front...if it feels too crowded, it probably is. And if it feels too sparse... either put one more in or wait for it to grow!
You can also propagate by cutting the stems and putting them in soil, they will grow new plants pretty easily! It will take some time, but it's a good way to save money