30 year movie making professional. Always trying to pack every image with as many words as possible.
Wow, you have a lot going on here. However, you haven't mentioned what your goals are for the footage. The final delivery; whether going back to film or staying as video, presented as theatrical or internet, etc., what type of effects you are going to process the footage through, and so on.
But to address your questions here are some ideas;
1) You need to research what type of street lamps are in your neighborhood. The manufacturer will be able to provide specs. though you'll still need testing.
2) If you are scanning the film then consult your tech. The negative IS your log footage. Discuss your goals (see above) and they should be able to guide you. For format, I find that I like ProRES best but that depends on your editing system. But note that 4444 footage is large and will require a fair amount of fast storage.
3) Get yourself a spot meter. You can refer to the exposure index on the film and then compare your readings to how you want the sky to look. (read up on the gamma curve for film stocks and how to expose for the desired effect.)
4) Pushing film stock is a chemical process and affects the grain structure of your negative. I always shoot straight and allow the colorist/transfer tech adjust in the transfer. Why add another variable to the film processing step. You'll get better control of the grain and an overall better look.
5) Refer to #2
6) You are asking about exposure. Use your light meter. The morning sky is different in different parts of the world and at different times of the year. (Film school should have taught you that.)
7) Your computer is probably under powered. What's important is the processing speed, processing power, software being used, and storage speed and capacity. Remember that when you edit your system needs to be able to process more than one stream of your footage. (Use the Blackmagic Disk Speed Test tester for insight; see the apple app store) 4K will likely choke on your system either because of thru-put to the storage or processing speed. You should be able to edit in proxy mode but the final will likely require bigger and better hardware.
Hope this helps
There are many techniques; green screen, angling the mirror, faking the mirror, painting out the camera in post... Each shot is a separate challenge and you have to be creative. But for most solutions, minimizing the camera's profile is the best place to start. Make it as small as possible and you may be able to angle it out and save on post processing.
I was there when Walter spoke in Boston and at the time he was right about the state of the software. But since then, the folks at Apple have made great strides in developing the FCPX. I do see it as the future of editing. On a recent project I was required to use Avid and I felt as if I had stepped backwards in time.
If you are looking to upgrade your thinking about the movie editing process, then take a look at FCPX. You may be surprised.