1) Lenses with wide aperture would achieve better video recording in low light. Would I need the latest lenses made for video recording, eg the Powerzoon series? Would using current lens system still have focus tracking capability for moving subjects?
Short answer: depends on the specific lens.
Long answer:http://panasonic.jp/support/global/cs/d ... ct/g6.htmlhttp://panasonic.jp/support/global/cs/d ... t/gh3.html
Also note that, the lower the light level, the slower and more unreliable Contrast Detect auto-focus is.
2) Direct audio recording into camera: I have been advised that separate post audio processing gives the best sound quality. Which software would be the easist to use ie just to replace audio segment?
A lot of folks, myself included, like PluralEyes
I would hope to record audio from Zoom H4N directly into camera, in uncompressed MOV mode so as to have the best audio quality possible.
Kind of a waste, IMO, since you'll still have to deal with AGC (Automatic Gain Control).
Given the choice of G6 and GH3, would the audio recording be somewhat similar if I am just using it to do basic video/audio recording without post editing?
Having said all of that, some unasked for advice: return/sell the H4n and buy an H6 (or TASCAM or Olympus audio recorder). (I personally use a TASCAM DR100 mark II and H6; upgraded from the H4n because of its relatively high noise floor.)