You can either do start at level 0, or just have them start at level 1 with their level 1 abilities, up to you (I started my most recent game out at level 1 because they were excited for their classes more than funneling)
At level 4 you get bonuses 2 and 4, another example, at level 12 you’d get bonuses 2, 3, and 4
You can go to 6-out-6
Fatigue goes away at the end of a fight
Don’t forget to check the Adventurers Options and Gamemaster Cyclopedia for some more content that might be relevant for the road ahead! Enjoy B4!