i am stenciling the side of my cake tier. i also wanted to luster dust, but was afraid it would look bad. I've done stenciling a couple of times, and use shortening to adhere the stencil better. I'm thinking that would look wrong with shortening either on top of airbrush or even if i airbrush after the stencil.

you can airbrush or just brush on the luster dust and letting it dry before applying the stencil, assuming you're using royal icing to stencil. That's how I've done it before.

I've never used shortening to apply the stencil, so not sure what you mean by this, I just apply the royal icing over the secured stencil on the cake, once it's all over, evened out somewhat, I carefully remove the stencil. I secure the stencil by using toothpicks or masking tape- or just having someone tightly hold it for me.