My fermenting sensei who taught us last Saturday said 1 teaspoon of salt for a pound of cabbage and he rounds down. Most of our cabbages were 2-3 pounds.
I was pleasantly surprised at how much the cabbage "sweated", once I started pounding it into submission. My sensie actually sells a wood tool for pounting, like a toy baseball bat, but with a foodsafe finish, I assume. Michelle (npub1n9h…4xgf) uses her stand mixer or a potato masher to achieve the same goal. My early kraut used a water brine. It's important that the water be unchlorinated (I use a water filter) because chlorine will kill all of our healthy bacteria. Also, the instructions I've seen say to use non-iodized salt, which includes many options like sea salt and kosher salt.
It's surprisingly simple. Just begin the process and then you can modify as you go along.