Piper, you can put your pot directly on a tiny fire. However, in many areas of California in the summertime, open wood campfires are not allowed. In some areas, they classify a Caldera stove as a camp stove, not as a campfire, since it is enclosed. Open wood campfires are kind of bad if it is windy. That is the beauty of the titanium Caldera, because you can burn wood, or alcohol, or Esbit. With the aluminum Caldera that you propose, you can burn alcohol or Esbit.
If you put a sheet of aluminum underneath the Caldera, you should be able to eliminate any trace of your fire after you leave.
Get the design pattern and study that before you start.
Aluminum flashing metal comes in rolls of various widths, lengths, and thicknesses. Start with a Home Depot and work your way out.
I doubt that you will find it to be super hard. Still, there will be tricks to be learned. You will probably need a hacksaw or some tin snips, and then some other tools. Air holes are normally drilled with an electric drill.