A model of 1000poly is nothing to the gold source engine, we had multiple 10k+ (up to 30 at a time) models in my 2010 CS server with out it crashing the server. If you manage to make a 3D skybox or ingame terrain and clip it properly (With a fence infront or something) you wont loose any performance. Go to russian map hosting websites and take a loot at some of their top rated maps there is even one with a whole industrial structure as a background model.
Asside from that, what do you use to generate models for gs? (always wondered how to easily go about that)