Dependencies between things and items files vs load order

That is because the node ID is how the binding tells the bridge what device it wants to talk to. Even if OH used different IDs there would still need to be a mapping to the node numbers which would likely change with a new controller.

Don’t make the mistake many do:
do not take a NON representative example just because that is the one you’re interested in.

You’re wrong there. Autodiscovery does not only get you the ID but a descriptive label, too.
BTW you can and should backup your ZWave controller, too.
You should read the Amanda README.

For things, there is simply no valid use case (other than to generate them from a script - but that’s circular reasoning then - noone needs that, it’s just CLI affine people that want it).
Things represent physical entities, they do not change fast.
Items is a different story hence there the recommendation to use .items files.

This has been discussed many times before and many before you have commented, you’re late to the show. Frankly, we’re all tired of this.
OH will move GUI, like it or not. You should start with GUI things now, not because it’s “better” but because files will stop working at some (unknown as of today) point in time.

A competing system, Home Assistant is already further along in that transition.