Just wondering
 

So I have been toiling away making templates for wheel skirts and trying to make a front grill block that wont make my car overheat.

Then I hit a major Snag... How do I even go about attaching any of this stuff? My templates have been nothing more than pieces of cardboard boxes and packing tape

Then a question rolled into my mind. Lets say I get her nice and aero, would swapping out for a lighter hood, quarter panels, and trunk lid, and rear bumper, have much of an affect if shes more aerodynamic. That is to say Will reducing weight help or be pointless at that point?

Reducing weight is always good and can help since you will have a better power to weight ratio.

To attach your pieces I think most people tape them down to start. Then once testing is finished they add mounting points on the back like using metal strapping and screwing the ends into the plastic shroud around the tires or use one of the mounting points for the shroud.

For weight reduction, it depends on how much city vs. highway you drive, as to how much effect you'll notice. Obviously, reducing weight will help both, but it'll have a more noticeable effect on city MPG than on highway MPG. You also have to ask how long it will take to recoup the cost of the lightweight body panels in the MPG savings.

My aero pieces are epoxy-reinforced fiberglass cloth, and I epoxy them in place. I also use screws. Black duct tape and coroplast is another good technique.

Assuming you don't use the brakes much, weight reduction helps only a little. But it's cumulative with all your other savings, so you should do it, but as a low priority.