This is a prototype of my setup. In the first image you can see 2 themometers. 1 for the automatic shut down, 1 to activate the mold. In the second image you see the weighometer that send a redstone signal when the crucible is empty to a 1tick pulse generator connected to the hoppers.
edit: Im not really sure if i understood the sensor trick. If you put it on top of the crucible, how do you drop item inside it? I noticed the hopper behaviour while testing, the item go stright down and that is really nice. Then you cant really put mold on the front becouse you cant put the hopper under it, it would be in front of the burning box.
edit2: i forgot to mention that you need a button next to the weigh ometer line to drop the first material and after that this setup is fully automated but you need to use saw/axe/gears mold if the recipe outuput is more than 1 ingot