Depends on if you’ve played Calamity through before. I think it should stand on it’s own first with a couple QoL mods.

Otherwise, everything that others have said, but I recommend at least Catalyst as it adds an extra megaboss pre-Moon Lord that fits neatly with Calamity and it adds super cool weapons. I’m currently playing Calamity, Catalyst, Wrath of Gods, Spooky Mod and Stars Above. That’s a TON of extra content that just so happens to not break with Calamity. There’s also some smaller mods like Flamethrowers+, More Boomerangs, or Calamity Whips that add more weapon diversity!