It sounds like you`ve got all the camera gear you need for the moment...
Story and good lighting are going to help you make a better film.
What do you want to shoot ?
The same thing happened when the RED first came on the market and lots of people became obsessed with ONLY shooting on the RED.
4K is a very useful acquisition format that provides more options in post, so I`ll use it when I can, but yes it does nothing by itself when it comes to storytelling.
If you shoot a lot of low-light work then buy the Sony AS7.
For everything else it's GH4 all the way...
- Internal 4K with 11 stops of dynamic range
- External 10-bit 4:2:2 4K recording
- Compact and fast native glass
- Can mount almost any lens ever made
- Supports a wide range of CODECs at bit-rates up to 200 Mbps
- Super fast low-light still-photo AF
- 12 fps still photo mode ( 7.5 fps with auto-focus )
- One battery lasts 3+ hours
- Good mic pre-amps on the factory fixed GH4 cameras ( most in store stock are the factory fixed cameras, there was a small audio-buzz problem with the initial stock of GH4s )
For now you can add on a Ninja Star recorder for $300 to get 8-bit 4:2:2 recording, and just wait for Canon to make a move. ( which probably won't happen until NAB next year )
Otherwise, if you've got too much cash in your bank account you could sell your C100 and buy the new Sony FS7 camera, which shoots 10-bit 4:2:2 in UHD to 60 fps and HD to 180 fps. It's the new queen of the prosumer ball at Photokina this year.
The original poster wants to shoot photos too, so the D5300 not having the optical low pass filter enables it to record noticeably more detail in still photos compared to the D5200, and it does not pay any penalty for this when shooting video.