I don't think this is a stupid question at all mainly because it's my question too! I did the same thing with the marker-I wanted to use a permanent one but the one I have has a thicker point and then I wondered. My sister gave me one sheet of template plastic but when I went to cut it because it was thicker I had trouble cutting it accurately on the line. I guess, we'll get better at this the more we do it. Next I am going to try butter lids because they are a bit thinner. I'm trying to work on my Farmer's Wife templates too.
Did you ever hear anything about Duchess? I'm still praying for her.
Good luck on the templates and I'll look forward to the replies from people that have done it before.