I don't think everything needs to go, but the biggest safety hazards at a glance are the plastic aquarium plants (they could snap off tiny pieces and fill up their crop with them) and the strings holding up some of the toy items (string shouldn't be used around animals as a general rule, as they will try to eat it, and then cannot pass it).
The cardboard items you made can be used when they're a little bigger, but I'd remove them for now, or reuse that cardboard to cover up more of the sides as those wire gaps are big enough for chicks to pass through (or worse, get stuck).
Most of the other stuff they just won't use, so it just takes up space. And they'll poop on it of course.
Not all of them, as long as OP gets one that does not have auto shut off it's fine.