Resistance is what you can measure with a meter, impedance varies with frequency, so you end up with a graph. you can measure inductance, which is what effects the tone, it is sort of related to resistance, since they are both determined by how big your coil of wire is. Overall, resistance is not a good way to judge pickups for suitability. Usually the higher resistance pickup is going to be hotter output, and in turn be darker sounding, but there are all sorts of exceptions. Noise and feedback are pretty much totally unrelated to it, being prone to feedback is down to how well the pickup is potted, from not at all to vacuum impregnated, which also effects the tone independent of resistance.