On the battery, any reason why you are using LiFePO4? As Lipos look like they are the standard now and they are not that expensive to be honest.
True but LiFePO4s seem to strike a nice balance between safety if damaged, weight and power output.

Just make sure you get one with a high enough discharge rating (C) PP3D website will help there http://pp3d.weebly.com/getting-started
Many thanks, it looks like the battery I've mooted using will fry the speed controllers (30C x (4.2ah x 2) = 252 constant, speed controllers are 85), so I'll find some lower output batteries and go from there.