Another windy explanation cut short, a DM in our group is planning on running a game where some of the characters are allowed (See: Encouraged) to play unusual type characters, within a CL limit. This includes things like normally nonplayable creatures, awakened animals, even a stunted/super young dragon.
That said, I'm planning on going for a quadrapedal type if I can. I'm familiar with the armor rules, but that's really about it. Without going into third party material, what sort of things work, or don't work well for a quadrapedal character that will be taking class levels?