The GH5 lets you choose different quality levels to capture your footage, so the size of 4K files can be the same as the Sony A7S II camera, or they can be about 50 percent larger when recording 4K in 10-bit 4:2:2 format.
Later this Summer the GH5 will get the option to record 4K video at 400 Mbps, which is about 2.5x bigger than the largest files it can capture right now. You will have to use the new V60 or V90 high-speed SD cards to reliably capture video at 400 Mbps. ( these new Vxx cards are also coming out later this Summer )
The C100 captures 1080p video at either 28 Mbps or 35 Mbps, so it's about one third of the size of the GH5 or A7S II 4K files.
A great film can come from anywhere and from anyone. Even the Hollywood legends produce unwatchable "turds" from time to time.
All that has changed in the past 10 years is the cost of entry to make a film has dropped so low that pretty much anybody can make a film, but it still takes talent and ideas to make a good film, and that is always in short supply...
The free clip browser app from Sony, "Catalyst Browse 2017.1" can open 10-bit GH5 files and transcode them to a different format like the Sony XAVC Intra formats which you can then open with several different NLEs.
I don't think you can get everything you want in one camera for the price you are after...
I would look at a used Sony A6300 camera which has terrible battery life, but it's pretty good on everything else.
If low-light wasn't necessary then I would look at the Panasonic GX85 which has 5-axis stabilzation in the camera body which makes a huge difference when hand-holding shots with old manual lenses. ( I bought one to use as my travel camera, and as a B-roll camera to the bigger / more expensive Panasonic GH5 camera )
So the C200 pricing starts at $6,000 for a bare-bones camera all the way up to a $8,400 kit with 24-105 f/4.0 lens : https://goo.gl/zYYfBG
>>>what types lenses did you use with the T2i in the videos above?
Sorry, that's not my work, it's the work of the very talented Kendy Ty who shoots almost everything with an old Canon T2i and a Sigma 30mm f/1.4 lens. It's amazing what he is able to do with a simple camera and one lens.