Re video, you can try `mpv --vo=sixel ${some_video_file}`. Apparently there are a lot of options to tweak that:
https://mpv.io/manual/stable
I do not know if mpv builds on 10.4 though. You may throw away whatever is optional in the portfile. If it does not, you may try an earlier version, just enable `libsixel` support. It was added here:
https://github.com/mpv-player/mpv/issues/2183
On 10.5 and 10.6 it should work from the existing portfile (in PPCPorts, not in upstream MacPorts).
You can customize `mlterm` quite a lot. To do it via GUI, build `mlterm +sdl2` and launch config executable with X server active. But GUI menu simply creates plain text configs in ~/.mlterm, so that can be done by hand without bothering to build GTK and X server. Color scheme, scrolling, background image, default font etc. – all can be set via config files.
Seems the same can be done via command line:
https://manpages.ubuntu.com/manpages/trusty/man1/mlterm.1.html (I did not try this myself).
P. S. Thank you for testing!