The best thing to do when working with Topsy Turvy for the first time is to freeze your cakes so that they are dense to work with and less crumbs when sculpting. Take your time and do it in stages and the whole thing will be fun and not such a headache.
I always make the bottom layer straight because it is more stable and I just think it looks more balanced in the end. I really ended up loving this cake a lot more after seeing it. It was fun looking and made a real statement.