How many circuits?

[muddpile]

I've decided to get a universal streetrod wiring harness due to the lack of stock and abundance of aftermarket electronics in my truck. One thing I wonder is how many circuits do I need? It isn't going to be loaded up with power everything, but it will have the following (on top of the common stuff like lights and ignition of course):
-Stock heater (may swap to vintage air)
-CD stereo
-6 piece electric gauges
-HEI

I think thats about it aside from headlights, taillights, markers, signals, ignition, cigarette lighter, interior light, etc. The company I am buying from makes 12 and 20 circuit kits. I'm not even sure what my truck has stock, or what I might need with my custom stuff. I know I will never add power locks, mirrors, windows, etc. Anyone have any idea? Thanks!