So I have only gotten to page 23 on the discussion board and 160 if you go backwards.
Here is my question: How do you dummy cakes?
I saw a few people who used spackle. some that did fondant and others that did shortening buttercream. which is better? Is this a good method to use to practice and to take pictures of rather then waiting awhole bunch of material and product and empty calories?
What exact method is used? Do I put plastic on the styroform or pans and then coat? Or what exactly?

It all depends on what you're making the dummy for! If you're making it for a display in your shop and it will be sitting out collecting dust, bugs, and bridal shows, then you definitely want to use lightweight spackle because it holds up the best of anything and you never have to worry about pest issues with them. Just remember if you go this route to only use those icing tips/equipment with the spackle.

If you're using it for an extra tier on the wedding cake, then yea, go for the same icing as you're going to use on the cake itself to make sure all of the colors match.

As for using just shortening based icing, the thing is, you want the icing on the thing to be something that crusts over because it'll help keep the fingerprints at bay.

One of the first things you need to consider is what you are wanting to practice --or what you plan to work in the most. Are you a fondant person? Buttercream? Stick to whatever it is you plan to work with the most and practice with that medium. As well, if you are just wanting to practice and not using a dummy for display or competition, then simply work with an overturned cake pan for things such as piping angles and borders. If you want to practice rolling and laying fondant, I'd recommend one of the cardboard "hat boxes" found in the wood aisle of your local hobby store. They make great substitute dummies and the cost is minimal as well as having many shapes from which to choose. If you are planning to compete or display and want to invest in Styrofoam, there are good sources from which to order and loads of tips on how to use them in the forums.

Keep reading those forums as well (at your own leisure, 'cause there's a ton of them regarding working with cake dummies...) Rae of BlakesCakes has great advice regarding dummies. She is a gracious lady and would probably not mind answering questions if you PM'd her.

Have fun practicing!

bc vs fondant depends on which method you want to practice/ display.
some people cover the dummy in clingfilm, some just apply the icing (once dried through it comes off, or dissolve in hot water).
some use royal icing or butter cream to fill any cracks.
before applying fondant, some people apply a proper crumb coat of bc, some just spritz with water or brush on piping gel.
really, its whatever you can be botherd doing, theres no right way!
xx