By that I mean placeables, plots, cutscenes etc. the stuff that you find in the palette window. Is it important you don't create too many of these? I have ~15min of gameplay (1 level) and ended up with over 60 different objects, about 20 which can be used again (I estimate). I got 2 of 3 levels left, I'm guessing the number would double or even triple before I'm finished.
Does it matter? How does it matter? Should I care?
I doubt there is a technical limit, and even if there is its not going to be very low. Something like 32k. Obviously you can't have thousands of objects onscreen or your fps will die and having many objects may increase load times, but you shouldn't be worrying about it with only 60.
I wouldn't worry. I don't know if there's an upper limit, but if there is, it is very high. Origins did not reach it, nor did any of the DLC modules that add-in to it. Thousands of resources is not an issue, so a few hundred shouldn't be either.
If you have a lot of resources though, put them into folders for organization. Otherwise it's hard to find them.