Nice project, my friend- I love that you're doing an early Yo!
Yes, the RS1, while being cool looking, will be so wrong for the ride of the Yo, which is an awesome ride, so long as the fork is right.
The only issue I have with the Litespeed fork is the rake, if it was more straight, it wouldn't look half-bad, (a color change for the fork would also help).
A Fat City BOI would be the wrong height for this frame, since this frame was not suspension corrected, and all the BOI forks I've seen have been suspension corrected forks, though I guess there's always an exception.
If you can find a Fat City Yo Eddy fork, it's a shorted segmented fork, and would ride and look perfect with this frame.
If you are unable to find one, may I suggest a Bontrager or Tange fork or Interloc/IRD expedition fork with the adjustable/removable legs and the four bolt crowns.
Perhaps a simple steel uncorrected unicrown with minimal rake.
ah, just a few thoughts, probably all stuff you already knew, but I look forward to your progress on this Fat