Bake at 325 b/c it is a very large capacity and at 350 the outside will be well done before the middle. It will take about 60 minutes for the large part to be done.
The capacity is about 10 cups, but use about 4C for the bottom and 3.5C for the top (or whatever gets you about 3/4 full) and as the PP said, grease and flour it very well.
A standard cake mix makes about 6C of batter so you'll need 2 mixes and you'll have some left over to make something else.
Here is one trick I have learned -- b/c the capacity of the bottom and top are different they bake at different rates. I'm sure DALESWIFE will attest to that since her experience as a pastry chef means that it's best to make sure everything has equal quantity so it bakes evenly.
Well, this giant cupcake thing doesn't have that, so here is the trick -- fill the bottom first and put it in the oven. Bake it for about 15 minutes THEN fill the top part and put the thing back in the oven for about 45 minutes. This gives the bottom part time to get started and the top won't become dry/over baked.
Check for doneness at the 45 min (total) mark, as your oven may vary from the ideal conditions at some lab.
Let the cake cool completely or you will have a mess on your hands. Remove from pans when cool. You will also likely have to trim the pieces so they are absolutely flat (mmm, something to snack on!) and align well.
Suggestion is to frost/decorate the bottom first THEN put the top on and frost/decorate that and add finishing touches. Easier to work with when the top is not on it.
Hope this helps.
