The only machine I know that uses 2 brushless motors on the same weapon is Toro Maximus, the Brazilian HW Drum Spinner. In a FW class machine there is no point. 1 is more than enough and 2 just adds complexity and cost.
Thanks now to Hobby King, powerful brushless motors are dirt cheap. A NTM 50-50 would be more than enough power. Combine it with a Red Brick 100A ESC and you are sorted. Total cost there, around £50. Power on 6S - 2000W!

Aluminium is good for hubs, the BaneBots ones are a great example of how it can be done. It does have its downsides but I would take Alu over plastic as it is less likely to get twisted or loose its thread/hold on a bolt which is uses to attach it to the wheel.