You’ll just install a pirated version of the base game, and then install there the pirated DLCs. Do not install them in your Steam folder or in your legit copy’s installation folder.

Try this, everything is bundled in one torrent and one installer: https://fitgirl-repacks.site/stellaris-galaxy-edition/

I’ve been using this site regularly for years, and it’s been safe so far.

Wherever you get it from. When you run the pirated launcher, it should detect your steam workshop items, as well as all your saves. That’s how I play Paradox games now, since I can’t afford their crazily overpriced DLC