Best way to improve my pizza crust Here's how I prepare the dough: 500g of bread flour + 325ml of water + 6g of instant yeast + 1tsp of salt. Mix with the dough attachment on my hand mixer for ~20 min, cut in 4, form them into tight balls, put into plastic bags sprayed with olive oil, store in the fridge. 

They then double in size in around 3h in the fridge and double again over the next 24h after that. They don't form any visible bubbles, its more like a very even rubbery foam.

I can start forming them into pizzas after those first 3 hours but those aren't that great, they aren't chewy or crispy, they are bland and mostly just taste like bread. 

48 - 96H is where the sweet spot is, great flavor, chewier, crustier. After 96H the dough starts to get sticky and hard to form though so I usually don't keep them that long. 

Thing is though, my pizzas are never as chewy or crusty as they come from a great restaurant. My oven is kinda weak, it only gets up to ~200C so I have to cook the pizza for ~15-20 mins, the less the chewier, the more the crispier, I usually aim in the middle but I never really get both. I also don't have a pizza stone, I prepare and cook them on parchment paper which I put straight on the middle rack. 

So do you guys think I would benefit from that stone slab? Or buying a more powerful oven? Or something off with my recipe or process?
200C is pretty low for baking pizza; you'll tend to get bread (as you say).  Commercial pizza ovens range from 300C to 450C
If you don't have a baking stone, then at least put the pizza on an inverted preheated baking sheet.  Something to get heat on the bottom of it, to crisp the crust.  Otherwise ... bready.
From the 48-96 hour period you're using, it sounds like you're aiming for a sourdough crust.  Why not create your own sourdough starter, and use that to start your pizza dough?