This was brilliant. It was a delight to divine the logic at each step, and even more fun to get to use it again and again. One of the more fun mini-puzzle hunts I've done. Great work, koo_koo.
FYI, I came here after I posted Playcebo's "12 Word Searches" (also on itch.io) to the National Puzzler's League Slack, and another puzzler posted this in response. Folks might like to try that word search puzzle series too.
Mike Selinker