Do I need to use fine silver findings with PMC?
Only with Original PMC, which must be fired at 1650° F (900° C). At this temperature, sterling findings will become brittle and might even melt. If you are using sterling findings, use either PMC+ or PMC3 and do not fire above 1450° F. It's also best to extend the firing time to at least half an hour longer than the recommended schedule. This will allow more time for the sintering PMC to fully diffuse into the solid sterling.
    Note that sterling held at these temperatures will always develop a thick oxide scale (tarnish). The best way to remove this is with abrasives like polishing papers, pumice, or Scotch-Brite. Tumbling will not remove this gray skin.

What is PMC Extender and how does it work?
Extender is a commercial liquid that can be added to any version of PMC to extend the working time. It does not affect the firing schedule or the resulting strength of the material, but it does lengthen the drying time. Use it sparingly, only a few drops at a time, or you'll make a clay that is difficult to join together.

What thickness should I use for a ring? How long will it last?
As a rule of thumb, I suggest a final thickness of 18 gauge B&S (1 millimeter or .040 inches). This would apply to either PMC+ or PMC3 and for both of them the shrinkage rate is 12%. This means you'd start out around 1.12 mm (or a bit thicker to allow for polishing). The lifespan of a ring will depend on several factors like the lifestyle of the wearer and the nature of the design

I want to include pearls in my PMC work.
What do I need to know and how do I attach them?

1. Natural pearls are discovered at random in naturally occurring mussels and oysters. These are the most precious and all there were for centuries. Except for small river pearls (Mississippi River Pearls), they are quite expensive.
2. Cultured pearls are grown in real mollusks in a farming-type operation. A sphere of glass or shell is implanted in the mollusk, which is then maintained in a net in the water until the pearl has matured. At this point the pearl is harvested, the animal is given a hearty "thank you," and the process is started again. These differ in the thickness of the layer of nacre, which is determined by how long they are allowed to mature.
3. Artificial pearls are made by coating a glass or plastic bead with a shiny material, often fish scales, mixed with glue.

You will almost certainly want the middle variety, which is used in the vast majority of all non-costume jewelry. The best way to secure a pearl is to glue it onto a post, or short wire. What you want is called a half-drilled pearl, and I think you'll find them from any stone dealer or jewelry supplier.