Sounds like you’re going in a good direction. Again I’ve personally never put anything like this together, I’d be interested to see what you come up with

Yes that was my main concern too. I suppose if you wanted to really go for it, you could also make cutouts for fans and cut some channels for airflow, but in the end aluminum panels with maybe some rubber standoffs for mounting may just be the safer option. And I suppose thubscrews for securing boards would make them easily removable

My mind for mounting personally goes to foam with cutouts (making sure the foam is of an antistatic variety). This would provide a snug fit for different hardware in their assigned spaces, plus easy removal/rearrangment, and in-built shock absorption in case of drops etc. Channels could be cut in the foam to allow different connections and route them where you need.

Now, I can’t say I’ve ever built a project like this so this may not work for your needs.

Yet another item on my list of why I’ll never buy a modern car.