I took the bed off of my 89 and I believe there were 8 bolts, the wiring harness for the lights, and the filler neck. But be sure to look out for the ground cable from the filler to the bed.
I do not know if it is legal or not to remove the bed, but they are not very heavy. My father and I just lifted it off the truck. So it can not weigh that much.
As for the gas mileage, be sure to check the injecters to make sure they are working correctly, check the coil, and make sure the valve in the air intake works properly. I had problems with these and it helped my gas mileage.