OR
you may be able to find a plugin that does what you want
cause now i see youre talking about order notes, which should theoretically be a feature many other people would also wanted or need with woocommerce shops
i was just more like looking at your points about thoughts on how to code this
but i bet theres a plugin for this if you can find it
or maybe even a standard feature that is shipped with woocommerce
https://wordpress.org/plugins/woo-order-notes/
how about this
