Thorium and Calamity are the go-tos for adding more content if that's what your looking for, I highly advise playing through Thorium first, since it's very friendly to newer players, and has a more vanilla+ style.
Calamity has a vast amount of fleshed out content, but has questionable balancing and is a lot more difficult, plenty of fun but might not be the best for your first modded play-through.

Alternatively there are plenty of other great content mods as well, those are just the main two you see all the time, some slightly less popular yet still very well made mods I can attest to being good are Spirit Mod and Mod of Redemption. There's plenty of other great but "different" mods like Overhaul (changes a LOT of the game's systems, I would play it on it's own if I were you),
and Cheat Sheet or Hero's Mod which are very fun to mess around with cheat mods.

It's also probably worthwhile to look for and download some QoL mods to make your life easier, I personally recommend Magic Storage and Recipe Browser, but you should mess around and see what you prefer.

Finally if you're willing to go back to 1.3, there's plenty of older mods which never got ported to 1.4 (or at least haven't been yet) like Ancients Awakened and SGA Mod which are worth checking out if you want something more archaic.

Oh also, I'm sure you already know but you'll need to download and use Tmodloader to run mods, since Terraria has no innate mod support, you can download it here on steam or manually through the forums, it's a easy download and from my experience runs better if installed manually, regardless it won't matter *that* much unless you are playing on 1.3.
Happy Hunting!

Edorbis is ok. It adds a little bit of content to every class and adds new bosses, new enemies and a new class (Engineer)

Try joining a server like pedguingames