Converting Nitro to Electric

[ADW]

Hi
I have a Caster ZX1R RTR nitro buggy which I'm considering converting to electric.

The Caster conversion is for 2 cells (2x 7.4v?).

Is it necessary to run 14.8V?
Is it possible to convert and run 1x 7.4V?
What would be a good budget Speedo and motor?
Is there any other manufactures that manufacture a conversion kit that would be compatible with the Caster ZX1R?
What type of cells would be necessary (allready have 2 x 7.4V 4000mA which I hope to use)

Any response would help,
Regards,
Alan