Here's one that I've hosted with 40 players - __SUPEREXPLOSIVE 40_Africas v2.2 [mods]:https://www.warzone.com/MultiPlayer?TemplateID=1423937
And here's one with fewer players but still a bunch, and also a ton of mods (better different ones than the above link) - __Safehold - Connected Commanders [mods]:https://www.warzone.com/MultiPlayer?TemplateID=1425648
Imho, both of these settings work well, but players who don't understand how the mods work can have issues, and notably with Connected Commanders, can even lose unexpectedly. Dutchman's Essentials mod could help with that, but it still requires players to (A) actually read it, and (B) understand it. Some mods change the mechanics enough that a quick read isn't sufficient to figure out how to play (or how not to).
@Belum - Even if non-members can't make modded Mega Games, they can join the ones a member creates. And with up to 300 players, this means a lot of people members & non can a heavily modded game.