I said in the video that xterm is a common terminal emulator. That isn't really true, few people use it as their default. What I meant was that it is basically included with every installation of X11 and thus very commonly installed, many people just don't use it.
I'm still pretty new to FreeBSD and as I'm perusing the Porter's Handbook, I'm realizing that it's generally ill-advised to use both pkg and ports at the same time. Although I haven't had any issues so far, I advise you to proceed with caution and expect breakage in the future.
I finally figured out why I ran into issues spawning st with fish like I show in the video... I forgot to NULL terminate the string so after I put in the following, everything starting working as expected
I also have a theory as to why st and vis were having SUCH a hard time getting along... It seems to me that vis either doesn't like st's default $TERM value or just plain doesn't like 8-bit color terminals. Although I suspect the former to be the case and this should be an easy fix by setting the default to xterm-256color, I actually don't like a huge lightshow on my terminal, so I set the following and vis started behaving:
char *termname = "xterm";
In case you want to have a look at my current configs and dotfiles, they are available at dist.qb1t.wtf/qb1t-dotfiles.