How may I establish a render farm over WAN? I'm using the blender network render plugin in the official plugin list. I have a few computers throughout the internet(WAN) that I am able to render on. Assuming I can get network connectivity(forwarding ports and other considerations), what kind of bandwidth requirements are there?

I have mainly procedural materials of 40 or so nodes, and only one scene. The .blend file is approximately 9MB. Will this file need to be sent once for each render slave, and each frame sent back? Or will more communication be needed that is not negligible? (I'm not using baked or cached simulations)

I'm assuming bursts of high activity when sending and receiving frames. Would this be true in practice? Or would other bandwidth considerations need to be taken?
The bandwidth requirement are highly dependent on your scene. With the official Network Renderer, you will need enough bandwidth to copy the scene file over to the each of the slaves (once), and then get the rendered images back (every frame). The communication overhead is negligible.