like everyone else, start off with a basic set and add as you build experience and learn about how you work. 36 years ago I started out by buying cheap but vary durable Stanley chisels. So the first set assembled was a 1/2, 1, and 1 1/2 inch, and added a 1/4 later when I started chopping mortices. At present I have 36 that range from 1/8 up to 1 1/2. They include the original 1/2, 1, 1 1/2 stanleys I first bought (the 1/4 died a premature death by getting snapped off in a mortice).
A basic range that I could easily get by with are 1/4, 1/2, 3/4 and 1. The 1/4 will fill the shoes of a 3/8 and the 1/2 fill in where a 5/8 would be more suited... It's nice to have a 1/8 and a 1 1/2 but I could easily taylor my work to avoid needing the 1/8 and the 1 would not be quite as good as the 1 1/2 in certain situations but would be adequate. In 10 years you'd most likely have triple the number you started out with...
Sent from the bathtub on my Samsung Galaxy(C)S5 with waterproof Lifeproof Case(C), and spell check turned off!