How can I molding small plastic parts for a model car?

I'm somewhat of a novice to building model cars, and I'm going to attempt to build my version of "Eleanor". The only thing is, there are no model car manufactures, as far as I've seen, that provide a model car that is exactly like Eleanor, so I'm planning on getting a '68 Mustang and making the details like windows covers, bumpers, and the side mufflers so at least the exterior somewhat resembles the car I'm wanting to build. What materials would I need to construct these pieces? I bought some MMD White Putty. Would something like this be sufficient or would I need some sort of epoxy to mold my custom pieces? I'm up for any suggestions!