What you are making is a pound cake. Or maybe a sponge cake, depends on the order of mixing the ingredients. Of the two, the sponge cake is somewhat lighter, so if you have been making pound cake (cream butter and sugar, add eggs, then flour), you can switch to sponge (foam eggs and sugar, add flour and fat). But both are hearty homemade cakes, they are supposed to be dense.
The iced cakes you get in a bakery are much lighter, because they use a different type of layer. Most types of cake are lighter than pound and sponge cakes. Try making genoise, chiffon, or angel food cake layers, they are all light. And yes, using cake flour will help too, or replacing part of the flour in the recipe with pure starch (usually cornstarch or potato starch, you can also use wheat starch if you can get it. Tapioca or arrowroot aren't that well suited). For a real "pro" taste, also throw in some lecithine, it makes the mouthfeel softer and smoother - but if you don't feel like hunting around for lecithine, don't bother, a good homemade cake doesn't really need it, I only mentioned it because you asked about "cake made by a pro".
There's really no point to freezing them, because once you take them out of the freezer, they start to accumulate moisture, which will cause the fondant to melt, or at least get all goopy, as you said. The only way to avoid this when you freeze them is to wrap them airtight, but you have to leave them totally wrapped until they thaw, so why bother? I would just air dry them for a few days and apply them to the sides of the cake. Better yet, why don't you do this with gumpaste instead of fondant? That will dry a lot faster and better and won't lose its stiffness when you apply it to the cake, so you'll get a more box-like effect.
I just used this method for a wood crate and found this tutorial : http://sugarsweetcakesandtreats.blogspot.com/2010/04/wine-bottle-in-crate-cake.html
I would to ensure it dries firm and is strong enough to stand on end. I can't remember the exact amount - I just added a little bit at a time until I noticed the color start to lighten, slightly. Once dry, I attached the panels to a fondant covered cake with a little buttercream. The panels stayed in place and remained firm. When it was time to serve, we just removed the panels and then began cutting.
the precolored fondants are so saturated with color, you can also add a little gumpaste to your black fondant without it affecting the color. Not sure what brand you're using, I'd used Satin Ice for this purpose as it will dry firm. I did for the panals on my shoebox cake and my Alamo cake - both times they were ready to use within 24 hours (flipping a few times during drying time).then measured the crumb coated cake and cut out the fondant panels with those measurements adding about 1/3" on both the front and back panels (cut the two sides exactly as measured).The panels dried for 48 hours (they were still a little flexible, but stiff enough to work with). then cut out four strips of black fondant and put them on the four corners of the cake (wrapped around the edge). it helped because any small gaps between the sides of the panels were largely disguised by the black underneath instead of white BC showing through.
I didnt have to re-cut/re-size the panels once appllied to the cake. I found that with the black fondant underneath and by simply applying or scraping off BC where needed to make it fit, it all worked out. Oh ya, I applied gumpaste/tylose glue to the fondant corners so that the panels fit nice and tighltly.
Best Answer
Since you say that you know they're edible, I'd say that the tooth and crown are most likely made of gum paste, not fondant.
The curves on the points of the crown would likely droop really badly if made of fondant because it never solidifies. Gum paste does. So, once you have it molded to the shape you want, you let it dry out and then it stiffens to a candy-like finished product. Here's an outline of the difference between the two and when you should use one over the other.
As to how to make them, the crown can be made by following any of a number of guides on the web. They generally involve cutting a strip of gum paste in the shape you like and wrapping it around a cylinder of the diameter you need until it dries.
The detailed decorations on the cake and crown and the crown on the tooth are probably made very easily with gum paste using molds.
The tooth itself will likely be the most difficult thing as it will take a lot of artistic talent and patience. Making figures is very complicated, particularly if you have no experience working with fondant/gum paste or with something similar like clay.
There are general guides here, though none of them are for teeth, they should give you an idea of how the process works.