In PoE everyone is a hoarder at the beginning. You get your first ring with 40 life and 2 resists and think it's the best ring ever, etc. Once you are more familiar with the game, you can be more discerning about what to keep. Most of the room in endgame will be taken up by small currency types, and even to experienced players it is one of the worst aspects of the game that needs several QoL updates. Not just the amount of small stuff, or items introduced by new leagues, but the stash management needs some work. (Why we still have id and portal scrolls in 2020)
If you are going to play for an extended period of time, say beyond casually trying out half the story once, I think the single best (and only purchase) you should make is: Get the First Blood starter pack for $20, it gives you a visual weapon effect and 200 points to spend. Then wait for a Stash Tab sale (they happen every few weeks) and use those points to buy the Currency Stash Tab + either a Regular Stash Tab Bundle (includes 6 regular tabs) + 1 Premium Stash Tab, or just a Premium Stash Tab Bundle (which includes 6 premium tabs. With a premium tab you can change its name and color, and make it public so you can easily sell stuff to other players).
From this point on, everything is optional or convenience only and up to each of us. Obviously the more and more you play, the more in need of stash space you might feel, but consider that everyone starts fresh in new leagues every few months, and you don't lose anything once the current league ends, it just gets moved to Standard mode and kept in a "Remove Only" tab until you take everything out, so it's never like you need more and more space the more you play. Once you get a few utility tabs, you basically have all the room you need for every new league.