wp_head() – list hooked actions with priorities?

While you can practically control order of hooked things by priority, it’s not always the right tool for the job.

In case of styles you should be using appropriate wp_enqueue_style() function which allows you to easily set up elaborate dependencies which will be automagically processed by WP to produce desired order of styles output.

Unfortunately while there is analogous wp_enqueue_scripts() for scripts, you cannot cross-depend scripts and styles like your question indicates. However it is common practice to not start JS execution until page has fully downloaded, so in most cases explicit depending on CSS should not be necessary.