Re: pickup heights?
There aren't any hard and fast rules.
If you get the pole pieces close to the strings you get a more intense sound from the tightly focused flux. Harmonic content is dominated by those harmonics with a significant displacement over the pole piece. You may get "magnetic weighting", caused by the magnets pulling on the string, causing false intonation.
Back the pickups off further and the flux spreads out. The response is less intense, the flux's footprint on the string is larger so the spectral response is wider (more harmonics). In short, the sound is more "acoustic".
Find the point you like best. If you play "dirty" most of the time you need to take into account that signal/noise ratio of the input signal is more important than harmonic content, so you are better off with the pickups closer.