How to best prepare Sukimono

I'm glad the kosher worked for you. I wouldn't say "avoid sea salt", I'd say "avoid fine salt". When you get right down to it, All salt is sea salt. It's mined from oceans dried up millennia ago, or taken from current oceans and evaporated. Kosher worked better for you because the crystals were larger. Some sea salt crystals are huge, Maldon, for example. It's a lovely finishing salt, you'd never want to use it for an application like this.

I would avoid iodized salt in anything involving fermentation, some people can taste it (or swear they can), plus the iodine can inhibit some beneficial bacteria. Here's a nice short article all about choosing a salt for fermenting.

Fermentation opens all kinds of doors to really good eats. Enjoy!

The kosher salt worked much better as suggested. I also did a batch using some ordinary table salt with a similar outcome.

I was originally instructed to use a generous amount of salt, which I think was simply easier for me to use too much of as I'd never made this before. As the cabbage is weighed down all the moisture comes out of causing the cabbage to apparently soak up all the salt a lot more than it would otherwise (or so it appeared).

In summary: kosher salt generously applied, but don't overdo it (avoid sea salt).