Well it really depends on the mood you're trying to convey. I would say the easiest way is to take your light panel and put it in the middle dash. This way it looks like the lights from the radio and such are illuminating their faces. You can also try getting some cheap USB LED lights and set those up in the visors. For power you would use a USB car nub in the DC power outlet. Those are probably the two cheapest ways I can come up with.
To get a ProRes export just go to the quicktime option. The first option is to choose your codec. Your situation probably calls to export a ProRes4444. Set your audio tracks and resolution. Then you should be good to export.
If he's just starting out I would say the GH4. Then spend money on other accessories for him like a mic, tripod, shoulder rig, lights. and extra batteries/data storage.
Might be able to hook him up with a nice lens as well.
I would recommend getting a mic, monopod, lite panel, and a variable ND. Here's some of the cheapest of the cheap.
Then the variable ND is going to depend on your lens. You can still get those for pretty cheap regardless though.
Well here are reasons to avoid 4k. Also regardless if it's fixed or varied, the max bitrate for all DCPs is 250Mbps. I have seen some messed up DCPs because people have tried to go higher than 250.
Also, theaters do have 4k projectors but a lot of them only have one. In NYC I can name a few theaters that have only one 4k projector. You can play a 4K DCP on a 2K projector but the image comes out to look like a high quality blu ray.
Does you camera budget interfere with your lens and light budget?
If so I would try the C700 and hook yourself up with lenses and lights.
If not go for the Alexa Mini. I prefer the image of the Alexa over Red. Red has done a lot of good work in improving their IQ, especially their highlight rollover but the Alexa still looks better.