Do a search for Coal Bin Pics and or Sizes.
Here is one threadHow big do you make a coal bin
You would have to ask Your delivery company, they vary from 2-6 ton, my guy usually does 4 ton min. but usually ends up closer to 5 ton, alway have a little extra in your bin for "Just in case". Also, different companies charge differently, so you would have to call them to find out. Probably anywhere from $200-250 delivered/ton depending on where you are.
Coal Size depends on your type of boiler, hand fed vs. stoker, etc....