@AbellaKellaher, this is really hard to define how many items is normal. This should depend on your computer performance and I’m not a specialist of computer. As my understanding, “Enable Object Hiding” will stop the game to render objects of floors other than the one you’re viewing. The effect is hard to note but it should make the game to perform better.
Certainly, if you find something disappeared while taking screenshot. You can turn it off if necessary.