In the models and media forum there is a resources sticky at the top which has the stuff you are looking for.
And Keith has some links memorized by heart for some resources and he might pop in here and post them.
Here is some software you will find to make FPSC easier.
Signs IV
Magic FPS
ECS
WCS beta
Decal Maker
As far as modeling software I use Milkshape to model with.
For $25 you can't beat it and you can use it to animate models as well.
The Gimp has already been mentioned for texturing and paint Shop Pro and Photoshop come to mind.
You will probably need Ultimate Unwrap 3D or UV Mapper to make UV maps.
If you search the forums you will find a variety of tools,apps,models,weapons,etc. to get you going.
There is a lot of free stuff available for FPSC.
I can safely say more free stuff than you will find anyplace else for any other engine.