Hey, those are some pretty cool experiments!
I like the red--seems to have some orange to it? That crackled finish could have resulted for other reasons, like painting when it's too cold out or having some surface contamination under the paint. You can use some fine-grit sandpaper to try wet-sanding it a bit, something at least 1000-grit and up. Just make sure to wash your hands before every time you touch this cover, as if you put any more paint onto it, you're depositing some amounts of oils onto the red paint. If you do wet-sanding, I'd rinse it off REALLY well with some detergent to wash off any sanded particles, as the color will turn chalky and splotchy otherwise on the surface, and then leave it to dry thoroughly. Then wipe it with some fiber cloth--I've found that paper towels leave some dusty fiber pieces on the surface, and I have to use compressed air cans to remove.
Anyway, after you apply your stencils and paint another color, you'll definitely end up with some raised edges, because the spray force is usually too high from rattle cans, unless you use specialized airbrush equipment. I'd cover up the part entirely, just leaving the spots you want painted in a different color exposed, and spray from a distance, misting on the new color. If you spray too close and start over the design area, you might end up with a lot of runny paint, resulting in seriously raised edges. If you start spraying away from the design and then gently sweep over that area, misting on the paint, and do that in a few layers, you should have better texture/smoother edges. I'd remove the masking/painter's tape as soon as possible after you paint-maybe an hour or two: just long enough for you to be able to handle the part safely outside of the freshly painted areas.
Sanding any raised edges is risky too, as you might end up chipping off the raised paint and end up with a jagged line. You can do a little bit of smoothing, but otherwise I'd just go over it with Clear. Either you can do a lot of Clear and sand that to smoothness later or just a bit of Clear for protection and accept some unevenness.
If you want stripes, check out your local auto supply stores. One of mine sells silver, gold, black, and chrome sticker stripe rolls in various widths, meant for car decoration. You can apply those under or over clear coats.
Sorry for the long stream-of-consciousness reply--just woke up
