Yup, pretty much as glooze says. Start with the frame component of the suspension assembly to ensure it integrates with the kit frame and to have something to build on. Then its cutting and fitting.
Don't expect the first attempt to be the final product. Even an experienced scratch builder likely wont do this in one go. If I were to scratch something like this, my first attempt would intentionally be my development mule, on which the lessons would be learned for the final product. It's a learning curve, but the only way to learn it is to jump in. Once you get going, if you have a specific question on how to handle a specific element of the build, question the forum. Good luck.