Well, first-level characters are already assumed to have some experience under their belt and, in most settings, are already more skilled and powerful than most people in the world. Zero level is pre-class.
I love level-0 games. I use the Dungeon Crawl Classics zero-level funnel and apply to 5e. Basically each player get four zero-level characters. In a way, because of backgrounds, it is more fun than DCC. In DCC you just have your stats and some equipment that make sense for your mundane background.
The idea is that most of the characters are going to die. Typically, the first adventure will either be a group of brave non-adventurers brought together by some event that would lead a fairly large group to come together to address, e.g.:
- A posse is put together to hunt down some baddies, free someone captured from the village, exact justice on someone who wronged the people of the village, etc.
- A sink hold appeared below Abe's house, and Abe and his house fell into some ancient ruins that nobody knows were located under his farm. A brave group goes to investigate and hopefully save Abe.
- A group of people of all walks of life is enjoying a traveling circus, which is actually a group of cultist who plans to perform dark rituals and human sacrifices.
You get the idea. In a four-player game, there will be 12 characters, in a 6 player game there will be 24, so it needs to be a scenario where that will work. It won't be a stealth job. The idea is that most of them are going to die. Of those that survive, you select one and choose a class.
I work well because it gives an origin story to the party that the players play an active role in making. It works best as part of a session zero so that nobody is disappointed if they were expected to come in with a 1st level character with a rich backstory written up and expecting to have plot armor protecting their precious, single character.