I made ellie's and used an 8x8 pan for one layer, and then cut that into 4 squares and used 2 or 3 for her cake. She could've cared less about the cake, but I thought it was the perfect size and it was easy and things I already owned
I would definitely go small - we got one for free w/the big cake we ordered and they sent a 6" round, 2 layers! I felt like it was waaaayyy to much, so I ended up cutting T a piece off of it to squish her hands in. The topper you're going to use is super cute by the way.
I think you can see it in my siggy pic- L's was a double 4" and it was cute for pictures, but waaaay too much cake! I don't think he even touched an inch of it, DH ended up trimming off the side L touched and eating the rest himself.
Re: If you ordered a smash cake...
Bronx Zoo: Summer 2013
To read my blog, click on the giraffe pic below!
DD#1 - January 2008
DD#2 - September 2010
Ds wasn't a "cake" per se, but a jumbo cupcake @ twice the size as a standard cupcake;carrot with creamy white vanilla icing.
Before
After