Please consider that I am asking these questions based on the assumption that I am filming rather than taking photos, which the rules don't really apply. These are just questions not saying you are doing it wrong just looking at your thoughts.
Any reason why you are not following the 180Deg shutter rule with your shutter speed by shooting at 1/100 and 1/400?
Also it seems that you are opening your aperture way up lending yourself to vignetting. I tend to never go that low to preserve a deeper depth of field and keep the image sharp by shooting between F4 - 5.6, my usable range is between F2.8 - 8 (Olympus 12mm). I am also using ND's to control light as well.
I never let my ISO go above 800 even at night/dusk I just feel there is too much noise. I have been running between the ISO 100 -800 however I think I am going to stop using ISO 100 and keep the range between 200-800. Can running the ISO down to 100 induce any more sensor noise in your opinion?
I strongly believe that ISO100 does not induce noise, it just lowers maximal dynamic range of your shot. So, ISO100 is usable, while ISO1600 is almost unusable, I agree. Please note that I shoot in 4K but mostly deliver in 1080p, so some noise gets smoothed in donwscaling...
180Deg shutter is just idea of what pleases average eye - depending on motion blur look you like and depending on motions in your shot, you can modify this rule freely. When filming landscapes I do not go for mortion blur but for clarity, where 1/200 shutter is common for video - look for DJI official guide how to set up GH4 on S900+Zenmuse and you will find 1/200... When I shoot close ups of moving cars or other very dynamic motions or close subjects then I tend to use 180deg rule (1/50) as well, but these are rare occasions for me... In some slowly moving evening landscapes I filmed even with 1/25 and got results which I consider nice...
When filming X5 in 4K I can not notice significant vignetting - because sensor is croped to central part (crop factor of whole sensor is 2.0 but sensor has more then 4000 pixels in width so for 4K 1:1 pixel readout crop factor gets to 2.3 or 2.4). Same applies to GH4. You can easily notice that additional crop when switching from 1080p to 4K... If one does not film fully even backgrounds such as clear sky, I find that regular DJI/Panasonic 15mm/f1.7 lens set at aperture 2.0 does not produce important vignetting with this additional crop (I did not test Oly 12mm, but I got similar results wit Oly 45mm). Depth of filed gets narrower, but consider hyperfocal distance at which you can stop thinking about depth of field - when X5 (and GH4) with 15mm lens at f2 aperture gets focused on 15m everything from 7m to infinity is sharp and clear - so I believe that f2.0 is good for landscapes where I do not ask for clarity of close objects which just fly-by anyway... For close up filming, when subject is just few meters away I tend to use f5.6-f8.0 as well (but then I use lower shutter 1/50 for motion blur, so I get aprox. same light)...
I find that you and me do not have significantly different practices: ISO 100-800 (priority 400), aperutre 2.0-8.0 (priority 5.6), shutter 1/50-1/400...
But there are problems with X5 which bother me much more then noise and dynamic range - custom white balance does not work, D-Log and Cinelike does not produce sharp images, some flickering in auto-exposure even in Aperture priority (when camera changes ISO and shutter in very fine steps)...