As for the key limes, they are smaller than regular limes and thrice as sour(in my humble opinion...). There are apparently people who freak out if the "key limes" aren't from Key West, FL but I assure you if you don't get your key limes from key west it won't affect flavor or anything. They are known as Mexican limes as well and can be easily gotten from, yep, Mexico and the Caribbean and some other choice growing spots. If you don't use key/mexican limes and choose to use regular limes however, I think that is just called a lime pie or tart. You can also use Key Lime Juice, which is available and made from concentrate. I think this tastes a little better than putting a gross, sour, semi lime-esq liquid in your pie. It makes my mouth sticky and me feel just a little sad. But it being your pie/tart it would be up to your taste preferences.
Oh, and in case you missed where the nuts went, we chopped them up and mixed them into the ginger snap crust. Yum!