Hello, thank you for your questions, I’ll try to answer to all.
1. No, there isn’t a courtesy message at the moment, it sounds like a good idea, maybe in the future.
3. The Reaction widget is available as shortcode and as Gutenberg block, so you could add it everywhere.
4. I don’t know KingComposer.
Do you know that there is a free version of this plugin? It works almost the same, but you will not be able to use your own images as reactions and there is no Gutenberg’s block (nor BuddyPress integration or multisite support).
Take a look here: https://wordpress.org/plugins/da-reactions/
Thank you again, let me know if the free version is good for you, and if I can do something to improve it.