You want to try to keep everything as low poly as possible and use the texture of the model to bring out details.If you are using a model for a static entity (basically scenery) you would want a really low poly count.
Characters and weapons are a whole different story and it is not unusual for a weapon or a character to have 2000-4000 polys or more since they have to be animated and require more details to function properly.
A lot of the models you will find on the internet will be too high poly for FPSC.While there are a variety of methods to reduce the poly count (TGC even sells a program that does this and some other programs have a similar function built in) the best way to insure your model is low poly is to make it yourself and keep it low poly.
Please have mercy and use the search function.
