I want to use the vacuum infusion method to make some flat panels that are about 1-2mm thick. I have attached a picture of what one looks like. My question is, do I need to make a mold for this in order to use the infusion method? I am just starting out so please bare with me and my ignorance. Thanks.

Just take a mould from it using signboard for the flanges. Should be pretty straightforward.  Just make them big enough so that you have space for the gum tape and the fabric.  It would be easy to use soric as your core and carbon tape at the edges (so you don't see the soric edge when it's cut), that way if you went for the thicker soric, you would easily get your thickness of panel without having to use a lot of carbon.