Absolutely, the texture will be very different than flour fried, but corn flour or corn meal is perfect for vegetables. Great corn fried vegetables include Okra, squash, eggplant and tomatoes.
Yes you can, I use whatever flour I have to hand.
You can use plain flour with a teaspoon of baking powder.
Yes, assuming that by "plain flour" you mean all-purpose flour. Because all three sound like the exact same thing.
No, because the shortbread will rise. You can use plain flour or rice flour instead though. it would be really nice.
Yes, it generally won't matter.
No. cornflour 'hardens' the mixture so it will keep its shape, normal flour doesn't do that.
not really because they'd turn out like muffins
The store mix has to list the ingredients and be specific. Wheat flour instead of Oat, Rice, Buck Wheat or some other type. Plain flour means all purpose, not self rising, cake or bread flour. All purpose or plain flour being wheat flour.
yes
That is 2.9 cups of flour
Not without some form of leavening agent. If you use regular flour instead of cake flour, it will be slightly heavier in texture.
I suppose you meant "turn8oz of plain flour into self raising flour". I found this on a website, hope this helps but hopefully you would have found it already.3tsp of baking powder per 8oz of plain flour = Self Raising Flour