Maybe htop? It’s pretty configurable and has decent bars for various resources.
Also if your reason for choosing pure TUI is just resource usage (and not the aesthetics of it / cool feeling / whatever else), then you could maybe look into running something like Sway or Xorg+i3 - those are very lightweight, well suited for single window usage, and open up a lot of possibilities for lightweight GUI apps.
It doesn’t. As the poster two levels up said, all bytes that don’t represent an ASCII character have the high bit set, even the follow-up bytes in multibyte sequences. So the condition
b >= 32
will match and preserve them.