Really just a fantastic 4x game. You can easily spend hours at once chugging away through this game. DLC is unfortunately kind of mandatory for a full experience, but you can probably get by without grabbing all of it at once. I'd advise Utopia for pretty much any player regardless of playstyle, and then picking a few other DLCs that speak to your specific interests (ie, synthetic dawn for machine empires).

Stellaris also has an active but somewhat disjointed modding community; since the game receives frequent updates, lots of mods break and never get updated. Really good core mods, like Gigastructures, usually stay updated on a good schedule.

If you're looking for youtubers to learn more about the game, I'd recommend Stefan Anon for quality strategic content, and ASpec for general information/game mechanics explainers.