This is point where I really wanted to be able to answer at least some of the questions I posed earlier.

“What is the difference between different kinds of icings and frostings and when is the best time to use them?”
baking911.com offers a lot of good information about this.  Essentially this is really dependent on the look and taste you’re going for. http://www.baking911.com/decorating/icing_glaze_choices.htm – Has a great table for this.  The most common icings are buttercream, fondant, and royal icings.  Buttercream and royal icings are best for piping designs.  However, there is a technique to roll buttercream, like fondant.  This often tastes better than fondant, but in a warm environment melts easily.  It’s also more difficult to work with because it’s softer than fondant.  Rolling a frosting is done to achieve a smooth look.  It often looks good, but not everyone likes the taste of fondant. Another icing must be applied so the fondant can stick, so those who might not like fondant can still enjoy a frosted cake.  Any other icing can be underneath – royal, buttercream, even ganache.

“What is the proper way to roll fondant?”
My books outlined this well, but I wanted this information to be on a website as well if anyone was interested. http://www.wilton.com/wedding/makecake/fondant/index.cfm – Wilton is a leader in the cake and candy industry.  This outlines rolling fondant and covering the cake. http://www.wilton.com/wedding/makecake/fondant/fondantamounts.cfm – this is a good table to see how much fondant you’ll need for your cake.

“When do you use fondant and when do you use gum paste for molding?”
Gum paste is used for making fancier decorations, like flowers, leaves, and more, and dries hard.  Gum paste can take a long time to fully dry, but when stored properly can last a long time.  Fondant hardens some, but never fully.  Decorations can be made from this as well.  Information from baking911.com.

“When there is a lot of weight to cake, when do you use rods to keep it up and when do you just use something like modeling chocolate?”
Dowel rods are essential for tiered cakes.  Rods help the lower tiers bear the weight of the upper tiers; otherwise, they would collapse.  Also, place them on a base that can handle the weight of the cake.  Also, dowel rods must be placed in the top tier if a heavier ornament is placed on it. http://www.wilton.com/wedding/makecake/building/index.cfm.  I’ve found that modeling chocolate is used to retain the shape or hold the weight of something.  On Ace of Cakes, I’ve seen modeling chocolate used twice.  Once, they make a cake shaped like a bull.  They cut fondant to look like hair and placed it over rolled fondant.  The weight of the “hair” was too much for the fondant so it fell off.  They then covered the bull in modeling chocolate and that could hold the weight of the fondant.  The second time, they were constructing a cake for the Hairspray premiere.  The cake was very tall, so they covered it in modeling chocolate to retain the shape and keep it from falling.  If fondant was used, it probably would’ve fallen off because of its height.

I’m so glad I was able to find answers to many of my questions.