also, if you dont want to buy more tools, just dril a few holes near the edge of where ou want to put a fan, then put your jigsaw blade in there and start cutting. i use blades with the highest teeth count per inch... which are coincidently also the best for cutting the metal.

as for templates, forget that crap, just diy, you really dont need a template to make a fan hole, a simple pencil and drill should suffice.