I like to go 4-6 inches of base (road base type material, sold as 21A, ABC, crusher run, 3/4 minus depending on where you live)solidly compacted, and then a thin layer of the decorative stone. You feel less like you're walking in beach sand that way.

Be sure to use a separation fabric (sold as Mirafi at stone yards) between the soil and the crushed stone; it'll help keep soil particles from migrating up into your stone.

Isn't the layer of the larger decorative stone going to feel unstable to walk on or have furniture, etc? Wouldn't it be more functional to make the patio surface out of the
more hard-packed stone fines?

If the area is to be rustic, out door camping feel maricinde is right on. I will keep that thought in mind as I would do this for a gravel pathway. I have never considered this type of material for a fire pit area. I have to agree with frankie. A more stable surface would be better for the reasons given.