Experiment with drugs in a really dangerous way.

so question if i got holt's uniform do i need some sort of holts hat?

is there any way to get higher holts curse other than the coat and visage? also does it kill you? worms sing in my brain?

Hi there
From personal testing, Holt's Curse only does two things.
One, by itself, i.e. you're just wearing the gear and that's it, it will induce minor psychosis effects (Broken ship equipment and hearing ♥♥♥♥ you shouldn't hear on very infrequent occassions)
Two, it enables Brainworms. From the Renegade Suit. Which is just Psychosis functionally, but it actually motivates you to do CaptainThingsTM like cigars and alcohol, so It's pretty neat!

SOUNDS LIKE A PERFECT THING FOR MEDICAL OFFICER (my name in barotrauma is literally psycho)

for a more specific explanation, holt's curse builds up over time wearing the renegade suit, and is multiplied by wearing holt's clothes, and has a few effects, firstly, random noises, including molochs, screaming, fractal guardians and chat messages, second, worm flashes which quickly add to the third effect, and thirdly, the worms, which are effectively psychosis, causing increasing view distortion and murmuring voices as it builds up