If you just want to give users access to WordPress dashboard, you need at least to set Read capabilities in Posts and Pages sections. However, when you want to give them access to a particular plugin, we don’t have a section for each plugin. Plugin authors can use any capability they want, including custom capabilities to access pages and services. If you know which capabilities are required to edit your plugins section, you can assign those capabilities to a user/role.
Keep in mind that many plugins create admin settings pages using a native capability associated with administrators, such as manage_options so in that case, you need to contact the plugin author.
When it comes to admin bar on front-end, you can use this code snippet to enable it:
add_action('init', function() {
if(current_user_can('custom_role')) {
show_admin_bar(true);
}
});
Best