I think your best bet would be to model the net as a sheet with a net material on it, rather than model each string on the net individually, as you'll get better performance from it.
As for the source-specific stuff, you'll want to check out the Valve wiki, since we don't really have much in the way of modelling documentation here.
You'll likely want to make it a prop_physics set to motion disabled in hammer (so it doesn't fall), and give it a grid of
jigglebones. Make sure you use
collision joints rather than a collision mesh, since you want the net to deform.
I hope this helps, I'm no expert on the subject of modelling for source by any means.