Kosher salt has fewer (or no) additives like iodine or anti-caking agents. It's just coarse salt that was used to dry-brine meats--a Jewish practice--and picked up the name from there. It's not necessarily kosher, or even Jewish for that matter.

I'll have to test my scale to see if it'll register small amounts of salt. It really is the only way to know how much salt is called for, especially since people are using a lot of specialty salts these days, like your flaky sea salt.