About the Death Star scene, I take that this scene happens some years after Vader gets his suit. We see that the imperial officers are all recruited and in full uniform, and I doubt Palpatine had thousands of spare uniforms hiding in boxes just waiting for his evil plans to be completed.

"I will form a galactical empire to make sure there's peace!"
*applause *
"So that's how freedom dies, with thunderous applause"
*appluse ending*
"And I have some cool, new uniforms for those who chose to work for me... I have 3 sizes... And you get this cute cap"
* Tarkin walks in, modeling the hew outfits *