I suppose it depends what you're going for, but in general I don't think being able to fully support some very old PCI devices should be the determining factor.
That depends only on their own project goals. Retro computing is a thing too.
Yes of course. If your goals are retro computing, yes by all means go ahead and use retro technology.
That's my point though: today, BIOS is retro technology.
It's also good for learning. But I agree that most of today's basic OS dev learning should rather be done with UEFI and/or Virtio.