Regarding various things...
I know it sounds blasphemous on here, but Rubies actually did a surprisingly good job on their ROTJ Royal Guard helmet. The
rest of that costume was varying degrees of painful, but the helmet was a very pleasant surprise. The only thing I needed to do to it was add some red lighting gel to both darken and red-tint the visor.
I know you already know this, but the AOTC, ROTS, and ROTJ versions of Red Guard are all different. I don't know how you wanted to approach this. The ROTJ seems a natural first offering, to go with the Original Trilogy slant of your offerings to date. I was surprised by Brian's book, and the info he gleaned from Nilo and Aggie, that the fabic for the Guard costume was custom-dyed. I know most things for the OT were, but I remembered reading at the time (and am still looking for that source) someone from the costume department saying they'd used theater curtain material -- which is available in that color factory-standard.
One thing, though, that I want you to examine with your particular care is the fabric itself. Most everyone says velvet, but the shine is off. The theatrical curtain supply house reps I talked to when trying to ID it over a decade ago all said, from the drape and shine (or lack of) and weight and such, that it was, with utter certainty, cotton velour, in the 18-22-oz. range. As you'll know from your research into Trek uniforms, most people hear "velour" and think of the shiny synthetic stuff, but there're a lot more varieties out there than just that.
I also want to know, from your foray into the Archives for this costume, whether the original opera gloves were the suede they look to be in test-fitting photos.
Lastly for this costume, the pike... The story persists that the main shaft was some variety of deep-water fishing rod -- same make and model as the hundreds that were used to detail the Death Star II reactor core. All of my efforts over many years haven't turned up anything, one way or the other. Likewise the source of the emitter tip. It looks to be a hob gear cutter on its mounting shank, but delving into early-'80s vintage hob gear cutters is not an easy thing.
Next order of business... The troops on Leia's ship at the beginning of Star Wars (I reject the label of "Rebel Fleet Troopers", as it's stupidity of the highest order to have uniformed Rebel soldiers on your ship if you're trying to maintain the cover of a consular vessel). Are you going to tackle these guys at any point? I'd line to have better options than the "close enough" approach of using BDU pants that aren't quite the right color, Navy workshirts that aren't the right color or construction, etc...
And third, I think my last PM to you a couple months back got lost in the shuffle.

Had a question for you...
--Jonah