I'm making a seated/lying down schnauzer cake for 75 people (rkt head). I'm having a hard time deciding what to start with: do I make 4 10" layers and cut them in half and set them on their sides so that I have 8 half-circles standing on edge? Or, should I do 4 9x13 rectangles and then carve away the excess? I don't want to end up with too little cake. and I don't want to make it too difficult for them to serve.

Any suggestions?

Or should I make really big ovals?

I would suggest using either the oval cakes or sheet cakes.

I know determining serving sizes from a carved cake was always an issue with me, but if you make yourself a pattern it will help you realize the finished cake size....which will then determine the size sheet cakes you need to bake.

I'm trying to avoid having to carve too much. I know that I can make cake balls, but I think that they're a pita to make and I'm more likely to just eat the scraps!

If I do the oval/sheet route, should I have a supported board half-way through? I'm thinking that it may be 8-10 inches high.

Yes you really should. The rule of thumb is: support for every 4" - 6" of cake.

I recently made a sort of Boxer-ish cake....I started with two 11x15 sheet cakes stacked...and carved it down to maybe 30-40 servings, and just froze the scraps for a trifle or something later. For a large 70 serving dog cake I imagine you'd need around 4 of that size sheet cakes. You can always piece stuff back together...I had to take some scraps and layer it around the dog's neck and head to get the right proportions.

Thanks guys! Kitagrl- the puppy's adorable!