Not sure about the design you're looking for...are you talking about a standard 6" round cake w/a fondant or buttercream pattern of the world on top, a globe style cake using a hemisphere pan, or something else? If you're going through the contemporary...I'm pretty sure you'll be limited to standard rounds. While they can do 6" cakes from what I've seen, I think they prefer an 8" from a design perspective. I've heard the GF is the best place to look if you want something beyond a standard round, but you may pay a premium for it.
As for allergies...DD6 is peanut and tree nut allergic. Make sure you indicate the allergy info when corresponding with Chef Brian via email. As for what you can't have... if it's only peanut...the peanut butter cream cheese and peanut butter cup should be the only things totally off limits, but he can confirm for you what you can and can't. The white chocolate toppers have cross contamination risk, but we've never had any issues with those. We've also had chocolate cake, red velevet cake, cream cheese filling, raspberry mousse, passion fruit mousse, and vanilla/choc. buttercream and been issue free.