A Furnace and a Mold

What is the most efficient way to make a mold/furnace for home use?

I am trying to experiment with metal-making, and I realized to see if my transmutation powder is working, I am going to need to melt the metal down in a furnace to mix it.

I would like to make a furnace with bricks or something simple. What is the easiest way to make one? Like a nice furnace that can reach 2,000 degress Fahrenheit.

Also, I need to make a mold. Someone told me I need to make a mold using the lost-wax process or through the sand casting process.

Can I just buy a mold online? I mean, I don't see the big deal, unless I am missing something.

I noticed online there are molds for different metals, why is that so?