This guy has a pretty good handle on setting up a group of PIs for clustering, so why re- reinvent the wheel?

Gigafyde - on Instructables

There are a couple minor gotchas, but overall, his is a quick easy read. When it's all done, I'll set it up so that the Leafs are communicating on the RJ45s to the head only. The head will have a second, WiFi connection into the world.