I dont know what that conversion is to inches but 10ft is max on artboard BUT you can always scale down and save as eps most vendors can scale back up if they need
Don't work in 50% scale. Work in 10% scale so you can simply move the decimal point for all your measurements, instead of doing math.
I can create a new maximum artboard size of 227.50" x 227.50" in AI cc.
How? What version do you have. I hace cs5