I'm making a minnie mouse cake tomorrow 3d head.
There are about 4 layers of cake which I've partially shaped.
2 questions
Do I need to use any type of support? It's not pound cake it's egg free.
Can I add to the shape using fondant under the final covering to make look more minnie like?
Thanks
A good rule is that you should have a layer of support for every 4" of cake. Plus, if you plan to make the base significantly narrower than the rest, I would put a board across the widest part of the head, and use pillars to support, otherwise, your head can fall over.
As far as putting extra fondant, it can be done. The only problem is most people don't want to eat that much fondant, so someone is going to get a big chunk of fondant leftover on their plate. Plus, fondant can add a lot of weight, so be careful that you don't get it too top heavy. Personally, if I need to add shape to a carved cake, I use extra frosting, then stick it in the freezer for a couple of minutes to get it to firm up before I cover it in fondant.
HTH 
I always use good old fashioned cardboard cake boards, which I cut to the size and shape i need.
I did a class with Pat Jacoby this fall and she recommends against using cardboard in the centre for support. I used to do it all the time too, but apparently it can suck the moisture out of your cake, get soggy from the moisture it has absorbed and then it doesn't really help you with structure anymore.
She suggested using foam core or something like that.
I've never cut served one of my cakes that had cardboard in it so I'm not sure how much moisture it would absorb though.
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