I have found that the welding data published by the electrode manufacturers is very close to results I have obtained. Get the deposition rates and % of deposition efficiency for given parameters. Figure your total weld volume plus a percentage (I use 10%) for variations. Now you can estimate how many pounds of wire you need.
Timing the job is more difficult, depending on position, welder access and comfort, etc. A study I conducted using data loggers showed that the average SHOP welder, doing run of the mill structural steel, mostly flat and horizontal grooves and fillets, had 1 hour arc time in an 8 hour shift. These guys were not slacking off. But obviously, considering many variables, your mileage can vary.
The Lincoln Procedure Handbook of Arc Welding is cheap in price and has a lot of useful info. (No, I don't work for Lincoln)
CHGuilford