Remember to always check your PHP Error Logs.
– js_composer: yes, it was used some time ago by Visual Editor, but not anymore
wplr-tmp: yes, totally
wpseo-redirects: if you are using redirections in Yoast SEO, you should not delete this
The plugin has been extremely optimized so now this depends mainly on your WordPress install and your server. With PHP, for each page load (and therefore for each asynchronous requests, in the case of my plugin), WordPress loads itself every time. All the plugins are also being loaded and might even run a task. Unfortunately, Media Cleaner cannot do anything about it. You can make it faster by checking out a few options, but the best is to enhance the system. I am trying to keep an article about accelerating WordPress here.
It would be too dangerous. A bad update, the page builder disabled temporary or another mishap and the WordPress install will be basically destroyed. So it’s better not. Also, having all this run in the background would slow down the install at times we can’t expect, might also crash and so it would need many debugging tools and screen to follow up the progress. WordPress was not really made for this kind of tasks and it’s better to avoid it with such a plugin as Media Cleaner.
There is now a setting for it. Have a look at the Media Cleaner settings :)