As fohat alluded to, when making it yourself you have a ton of options about what to put in it. If doing it properly, the only consideration is having a VERY clean kitchen, containers, and tools. It's like homemade yogurt, sourdough, beer, kombucha, or any cultured/fermented food. The healthy and safe bacteria and fungus will out compete the gross/dangerous ones, but only if they get a good start. This is especially true of kimchi because you aren't using a starter culture (but you can, and some do, it gets things going faster).
So clean bowls and jars, keep veggies submerged, ferment on counter (not in refrigerator, it will take forever). Fish sauce is there for the glutamates (which is why MSG is added so often), and glutamates are tasty. If you don't want fish sauce, boil some kombu in the water you will use and you're golden.
All that said, I don't make it at home. I have multiple food co-ops and vendors at farmers markets nearby who make great stuff making not worth the effort.