Also if you go to the generic browser in the editor you'll see a statistics tab. This will tell you the amount of polygons in an entire level (not the amount displayed). It also has other helpful info like the number of instances of certain assets or the amount of tris for individual assets.
yeah just keep it a nice amount, not crazy amount if it's going to be instanced much, then build it all you'll be fine as long as your art is good, then that sort of thing won't matter so much (but definitely keep sensible tri counts!)
The biggest hitter with UT3 is not the amount of triangles that you have on the screen at one time, it's your material setup and texture size. While triangles do have a cost to render, materials(Usually) cost more due to complexity and texture size. Remember that for every material ID a mesh has on it, that mesh has to get…