I use this plugin on my own Discourse site (but not all features of it). I am going to support the plugin for both ESR (which I run) and the latest Discourse release. Both those releases are tested against in the project setup. These tests run at least once a week if those versions change.
Currently only the Ruby side of the plugin is automatically tested (almost every little part of it). I still need to work out writing sets for the javascript side, which I plan to do eventually.
No issues with that. I’d also welcome any suggestions for adding extension points (e.g. plugin outlets for theme components, or events for plugins)
The dashboard is available to all visitors.
I explicitly did not create something to add the ko-fi widget to arbitrary locations. I think that can be done via a theme components, much like your progress bar component. The kofi_account account setting is available for the client, which should be sufficient for any kind of widget.