The colorlight 5a-75b together with Litex is a great way to get started for cheap.

If you want something even more basic, https://github.com/kingyoPiyo/Pico-10BASE-T is very simple.

Layout for most consumer standards is pretty lax, almost anything will probably work.

Would this even be possible? I assume some devices can do PD both ways (for charging and as a source). But if that’s even possible, I’d imagine it to be rare. I’d love to know the case from someone who knows more.

The problem is that not many USB-C data ports do PD, and even when they do, they may not necessarily provide the voltage required by such disk.

And more importantly, what do available chips support? How easy is it to get chips that support PD + data?

This isn't my area of expertise, so I was hoping someone would be able to say -- Yes, it's possible, I do this all the time. Or -- it's theoretically possible, but not widely supported, so no one does it.

Two of the USB-C ports of my Dell XPS 13 9380 provide 5A/3A over PD, and the third one provides 5A/1.5A. All of them can negotiate both sink and source PD contracts.

If your laptop can be charged via USB-C port and you can attach peripherals to the same port, it's almost certain that it can negotiate a source PD contract as well. That doesn't automatically mean you'll get more than 5V though, so such PD port may still be useless for powering a disk drive enclosure without additional voltage regulation.

Many PD controllers support this for 'sourcing' (5V/1.5A or 5V/3A) natively, since it's a common use case for laptops.

Your first designs may or may not pass a radiated emissions test, and it may or may not work reliably if you want it to fly through the Van Allen belts or in an industrial panel full of VFDs, and you might want to aim for last year's implementation rather than the bleeding edge. While it can be made complicated if you want to truly and thoroughly understand it, just following basic rules of thumb can go a long, long way.

At some point you're already applying all those rules of thumb, but how do you then actually measure what works and what doesn't so that you can improve beyond that?

It seems it is difficult to find resources teaching that, and also the equipment needed becomes very specialized and expensive fast.

But after 10 years in the field, I've sadly forgotten most of that and learned pragmatism instead.

(Benson Leung is probably having a bad dream right now.)

They go into problems of high speed circuit design in general, and the high end gear and insane debugging skills needed to do so!

See their Twitter, or Spotify (Oxide and Friends) - eg "tales from the bring up lab".