Find my Russian vapes fantastic driven at 30 watts. Believe the build is around 1 ohm, but using the futura for me power plant. So by my way of thinking is that as long as she wicks good enough, sub ohm is not a prob. Don't know what the top end of the Kayfun style atomizer is, but 30 watts is not it. will see once Max arrives.
Far as getting the target ohms, tis best to find out for your self as you learn to build, and yeah an ohm meter is required equipment. With mods like the DNA30 out, I don't focus oh target ohm rang anymore, look more at designing the optimum build for the specific atomizer. Then just crank it to the max.