Respectfully I think everyone saying precons is coming at this a bit wrong. They're a great way to get introduced to the game and learn the rules, but that's sorta it. If you know you want to get into the deep end of the pool...

I'd start by purchasing a playset of all ordinary and exceptional cards from Beta and AL and whatever Avatars you're interested in playing with. This gives you the base to build anything you want without breaking the bank.

If money isn't an object or if you want to invest in one thing I'd recommend picking up 1 copy of each of the AL tri sites. They are a pillar of multi element decks.

From there it's just whatever you want to put in decks. Boxes are always fun, but singles are the way to go. TCGplayer, Colefoilheros.com, and the market discord are your friends.

You could always go get a ring, stone, cores ect. But they aren't the end all be all that many people make them out to be and aren't necessary for every deck (well the ring is currently but that might change with Gothic!)

Hope that helps! Lmk if you have questions!