It's actually closer to 1.8x, not that it really matters since the difference between MFT and APS-C is so minuscule that it's not even worth considering.
Stick to vintage lenses. They are almost always better than modern lenses for video in every regard: more durable, smoother focus ring, cheaper, more "painterly", and many vintage primes aren't a ridiculous size like DSLR lenses.
For a zoom get a Nikon 80-200 f4, but make sure you use a lens adapter with a tripod collar or else your footage will severely suffer.
For a UWA, I prefer the Olympus 12mm f2 in every regard except for my opinion that 12mm is far too wide for follow cams. The Tokina 11-16 is also a great lens as it has more economic longevity and variable focal lengths, but the size on a GHx body is awkward without any supplemental grip equipment.
For a wide prime, the Lumix 20mm 1.7 is one of the best lenses I've ever used. Excellent color and sharpness without feeling stale or artificial, and the pancake size makes it a quick-draw lens, which contributes more to good shots than most people realize.
For all else, look into Nikkor and FD primes. Don't spend extra money/space on that Rokinon/Sigma crap.