Personally I wouldn't chop up the barrels or the plates. It's unlikely to cause any significant visual artifacts, so it's not worth the additional work and polygons. However, it's a good idea to test the prop in-game. If it causes trouble, remodel it and test again.


About z-fighting: when a polygon is drawn, it's translated into a bunch of pixels on-screen. For each pixel, a depth value is stored. When another polygon is drawn, it checks these depth values first, and only overwrites a pixel with a lower depth-value (e.g. a pixel that's further away). However, this z-buffer isn't infinitely accurate, so when polygons are almost equally far away (and the further away they are, the more likely this problem is to occur), the result is sometimes that pixels of both polygons are drawn through each other.