I've already quickly blocked it in to the scale I want, and started to make the bigger details and trim some of the fat. I don't want to have too much brush work, as I'm going to be making an entire set of textures to make up most of the small details. It'll also be cartoon style textures, similar to Team Fortress 2 and Borderlands.
I've already done textures in this style, though it was mostly just me messing with it, but I feel confident now I can make something spectacular. Here's a small example of something I did quickly a while ago.
As for the level progress itself: