Those bulk cards aren't a terrible way to get a collection started, but honestly more often I'd recommend just going to drafts if you can. They're pretty cheap, you have some fun playing and learning the game, and you come away with a nice little set of cards you've figured out how to play over the night. If you're going for casual play a box of those random cards is a place to start, but nothing beats actually playing with them.
Theros is an interesting beast honestly, because it's a plane that has a ton of really great moments, but very little cohesion to make it feel like a real world. It has lots of cards that are great mythological references and all the gods are excellent, but the actual plane feels super sparse outside of them. There's only like three or four cities total, and it ended up kind of mismanaging some of its mechanics. Still, it's an interesting plane, it's just a pity that it's got a lot of stuff in it that feel a little half-baked.
Fucking 10/10 star aesthetic though, holy shit was that a good idea.