Okay, after three attempts I managed to run the mod via Knossos, except this time it downloaded the April 12 build despite having clearly set it to RC2 at first, then I realized it also forgot I added the MediaVPs as a dependency (for the seventeenth time in the past 24 hours), so I readded that, but a clear whole delete -> redownload from Knossos -> "Play" successfully ran the mod, with the April 12 build, but it runs.
Thanks for the help. I appreciate it, even if I'm entirely worked up over this.
Can someone check if they can run the mod, with MediaVPs and a new FSO build?
I'll add the Knossos link to the OP once someone confirms it works as intended.