The only foil I use is Venture Brite-Bak foil, which is a thin but strong foil designed for stained glass artists. Why? It has a strong adhesive backing and is the most trouble-free foil. As to design, most foils are put on the bait and THEN textured to represent a scale pattern. Many of us use a knurled tool handle for texturing. I usually use the little knurled knob from some Vise-Grip pliers.
There are different schools of thought about painting over foil. Some guys like to clearcoat the bait over the foil, paint, then re-clearcoat the bait. This is the safest method because you can easily wash off the paint if you goof it up. I usually just apply paint directly to the raw foil. Acrylic latex paints from Createx and many other companies come in two versions: opaque and transparent. use the transparent to maintain the foil's reflectivity. You can either custom mix the colors you need from the basic Createx palette, or just spray one color over another to blend the colors. Hope this helps.