Second Life textures

Gold is hard to do as a texture, without the metallic sheen gold is just a kind of dull yellowy colour so using just a texture is always unimpressive in a 3D environment, the trick in SL is to use a low or medium shiny effect on a fairly bright yellowish metal texture, and add a little of the glow effect (usually not more than 0.1) to brighten it.
Using twin layers of texture, with a shiny surface, then a partially transparent texture on a layer above it can give a nice effect too.

It's not perfect as Second Life doesn't support the fancier metallic specular effects that better engines do that you'd need to make a really good gold look but you can get a decent look from a bit of tweaking.

Yes, making a slightly larger shell is the way to do it, although I have heard that if you make two objects of identical size and position and set one to have a solid texture and one to have a transparent texture then the transparent texture will always be seen on top, though i've not tried that.

Whether an object is mesh or prim has no effect on the textures, you should be able to get the same effects on any object, however shape affects how well reflections will show, slightly curved surfaces show reflections a lot better.