To minify CSS and JSS you have some options:
- WP Fastest Cache (if you just want a free plugin, it also includes a paid version)
- WP Rocket (Paid, but you can find it here in Babiato for free)
They both should be fine to help you with CSS and JS optimization, and caching in general.
For image compression you could use somethink like Smush, but i recommend you to optimize the images with tinypng.com before uploading to your Wordpress, i think is the best practice.