and they're unanswered, too.

I agree, your method is not a big deal, nor is multiplexing, but for a small display, in this case, only ten characters, multiplexing is pretty easy and cheap. 7442's cost about 18 cents here, and are probably not much more expensive elsewhere. I made a display of this sort (16 characters) a couple of decades ago, using an MCU and a handful of decoders. The parts are still readily available for nearly nothing.

What puzzles me is that nobody asked about the response time of the LED's, and about the LEDs' current/brightness relationship.

I'm sure your approach using dedicate hardware will work just fine, but I'm also sure the old, tried-and-true multiplexing will work. I'm guessing that 7 7442's or maybe LS145's will cost less than US$0.03/LED. Let's see ... ~US$1.40 divided by 420 LED's ... hmmmm ... and, oh, BTW, they're in an easy-to-use-in-a-prototype, DIP-16 package ...

RE