I had a setup where i would grind infinite cobble from the Ignious Extruder into sand, auto craft the sand into sandstone. Then I would have that get ground for the niter.
I had a similar setup for grinding netherack for sulfur, but that was the more manual side as I had to actually go out and get that. As for the coal, I power my stuff off an auto treefarm + steam dynamos running on charcoal so that was no biggy.
Now that I have hit more end game, I found it far easier to shoot a wither in the head with an M60, make a portaspawner, goto the moon, and steal the evolved creeper spawners (Though be careful there's some glitch going on where they will say they are one type of spawner and look like that spawner type, but they will spawn a different type of mob and when picked up the spawner will change types to the mobs it was spawning. So to be safe find one that is actually spawning creepers.)