If you can use 18ga use that. battery, atomizer, switch if wired direct, for the pot/trimmer you can use the thinnest wire you have. I use 32ga on my pots 18 everywhere else unless if using a mosfet or pull down pin 1 use 22-24ga gauge on the switch, 18-20ga on batts atomizer.
If not heavy subohming 22ga is fine but for killer full output 18-20ga are recommended.. If using solid core 20ga great for anything you
throw at it but its not the amp hold its the noise/resistance in the line resulting in v-drop or v+up from your dialed setting.
I use 18 and 20ga. route it, shape it, solder it..
Here's the chart we mostly use less than 7" so its a bit better in numbers, not much tho..