Only able too answer #3.
3) I don't have exact numbers and I know it varies a little bit dependant on type of coal. Generally speaking pound for pound I've always heard coal to roughly have twice as much BTU pound for pound than hardwood charcoal.
I used charcoal the first few weeks of forging. Once I got my hands on a 55 gallon drum (400-500 pounds worth) of WV coal, I never want to go back. Coal can actually hold your work in the fire.