About lighting fires, these aren't really spoilers, but if you want to figure out absolutely everything on your own, don't read.
You can draw a bow with a normal arrow, hold it drawn, walk up to a lit torch or anything on fire, light it, then shoot at whatever you want to set on fire. You can also hold a bundle of wood and a piece of flint, drop them, and strike the flint with a metal weapon. There are torches to pick up all over. They work as melee weapons, but don't use them in combat.
So you got a Switch too, gpw? Nice. Kinda jealous. I'll be curious to know how these hold up over time.