Have a good long think about “basics” (solid-colored shirts/skirts/tights, simple dresses, classic pants, etc.) because you can build most styles/looks from a good collection of basics. Those are what you should be investing in, if anything – not random extra pieces that you’ll only wear rarely.
For example, a solid-colored pleated miniskirt can be styled to look punk (torn tights, oversized band T-shirt, leather boots), preppy/schoolgirl-y (collared shirt, opaque tights, dainty shoes, maybe a layered sweater or a necktie), 80s eclectic (off-shoulder sweater, tights, legwarmers, flats, neon jewelry), and lots of other ways. If you have good basics, you can do a lot.
I’d also recommend that you think about writing some kind of “style statement” to unify your favorite style elements into one overarching theme, and then take it with you when you go shopping. It can include pictures as well as text descriptions and a list of things you want to buy.
Pinterest is also a fun way to put all your style influences in the same place.
I don’t think there’s anything inherently wrong with jumping from style to style, though. I am certainly guilty of dressing as different archetypes or “characters” on different days. If you have the closet space, it’s okay to slowly build up your wardrobe over time to a point where you can basically dress however the hell you want every day. And, again, this will be easier, quicker, and cheaper if you have a great collection of basics.