Lets say I plan to shoot 4k mostly. I was thinking about this workflow..
Mac Air 2014, 4gb RAM

i don't plan to upgrade & i have no problems leaving pc in cold air for whole night for final render.
- shoot & store on 3TB USB 3 drive
- create 720p or lower res proxies - potential big time loss
- Edit in Adobe Premiere CC using proxies
- Export from Premiere to prores 442 or some intermediate codec, maybe downscale to 1080p
- grade in Resolve

- final export from Resolve to h264 encoded file
Is this bit overkill? I just started to understand codecs so any opinion about this workflow would be greatly appreciated.
Thanks!
There is nothing wrong per say with this workflow but for example color correcting using BlackMagic Resolve on a h264 native item (and believe me, once it's h264, you can make it ProRes all day but contrary to the argument, you can not increase the quality of the video. It's at its best at h264.
It's analogous to putting a fiat in a Bentley and calling the Fiat better while it sits in the Bentley. When you take it out, it's still a Bentley and h264 native is still h264 color space and all if you put it in a larger wrapper (ProRes). I am sure someone will scream and say I am wrong but trust me, I wish I was but am not.
Anyway, color correct in your editing software or AE if you're bringing it in there.
Also, why proxies? I can run multiple UHD streams in realtime using the latest iMac. My friend is doing the same on 2014 iMac. I have 64gb ram and new skylake chipset but I'm blazing with no proxies.
Most editing software for 4K will only show you one field (two in each frame) when it is doing "realtime" so it's a proxy anyway in reality.
Good luck. Don't overthink it. Your workflow is WAY too complicated.
Edit: just read it again and yeah, the outputting your master as a 422 ProRes (not HQ btw) is the way to do it. But that should be your final move.
Grade it in PP. You DO NOT need to bring it in to Resolve at this point. If you are just learning about codecs, I would keep it simple as there are plenty of excellent color correction controls in PP.
As for your proxies, I don't think you need to. Even in an Apple Air which is admittedly not the strongest machine for video in the world, I think you'll get at least one "realtime" 4K stream, maybe 2.
Let us know.