Yeah, proportions are just whatever feels right. It's hard to mess this up too badly. Too much salt is the only risk, and then it's probably only a big deal with spongy things like mushrooms.
I try to marinate for an hour or more. Three days isn't too long, but there's a point of diminishing returns. Some people vacuum-marinate, but I haven't done that.
Gochujang is a paste of korean chiles and soy and whatever other stuff. These days, I can buy it at any full-service grocer, or you could order it:
https://www.amazon.com/s?k=gochujang
The Sichuanese pickles that I purchase are pictured below, but you could also blend
pao cai and chile oil for a similar effect.
Also, I neglected to suggest dark sesame oil. It's like lime in that you can mix and match it with anything. Miso is like that too, to amp up the umami.