Yeah its fun doing it from scratch.
Viewing post in Github repo with my clojurescript game starting point
Yes I'm using shadow cljs https://github.com/thheller/shadow-cljs
You run the release command and it builds a production build. Then you zip your public directory and upload it to itch. I just tested it and you need to use relative paths to get your assets to load when running on itch.
When developing with shadow it starts a web server for you and it automatically builds when you save a file.
You can use other build tools too like figwheel but I think shadow is more maintained.