At 18 ct. I would use petite beads, which I don't think would really fit
if you did it 1 over 1.
Thanks Joan for your input! You know I didn't even consider how the beads wouldn't fit if I stitched it 1 over 1. So that's out, because there's no way I'm going to do a mirabilia without beads.
I spent last evening and this morning himming and hawing about that peach fabric in my stash, and ultimately decided it was just a touch too close to the fairy's skin color. The fairy's face is back stitched (which would help it stand out), but it's still just too close. This is what I'm thinking of going with instead: