I just watched the craftsy class about the 3-d dog cakes, and she uses a mold to do the fur. But you can just use a 1/2 and 1/2 fondant/candy clay to cover the dog, then use a tool to mark the fur on the cake. The candy clay in the fondant will keep it from drying out and give you some time to work the marks in.
the pan sizes would depend on how many servings you'd need to get out of it. I don't know if this will help, but I did a blog post about a pug cake and you can see the shape of the cake before I covered it with fondant. I think I probably used a couple of sheet cakes and some small rounds to do this one. http://acaketorememberva.blogspot.com/2010/05/cake-design-pug-grooms-cake.html