you know toon planets are quite simple to create, the problem is getting the style right.
You've basically gone and extruded faces really, if you look through the tutorials the 'game' one has cartoon style buildings; while cartoon styles greatly variety.
Personally how I'd do this is to create myself the sphere, relatively low, 12x24.. you use this as a template really for the time being and create a bunch of Boxes on it using the Grid System, this will allow you to create them around the hull of the sphere.
They'll appear on top for the time being, so change the axis to local and then you'll be able to change the hieght so it's inside.
Something more interesting is you could create the buildings seperately, then use the Grid System to then place it on rather than creating it on it. In this fashion you can array a number of buildings on it and then simply resize them to give variation.
If you use a Toon Material, you'll find because the ends of the buildings are inside the planet you'll only have the outlines upto the surface. It works as a very very good effect, if you need anywhere as a line in the toon material on the sphere itself or the buildings, simply select and seperate the edges. Don't move them but seperating them will cause them to create thier own lines, if they cross into each other they may disappear and if they are overlayn at given angles you'll get 'portal' gaps where you can see right through the mesh.
Max comes with a huge number of tutorials though
