It's all in personal preference, I for one like FM8 because well I like to experiment with different synthesizers just to try them out and get different results with synths. As for the post processing, the fx chain I had for that growl is pretty large but it's an old synth and I used to use a lot of post processing back then. As for the random stuff it's sort of just diving in and trying out a lot of different methods and processes, it's good to come up with theories as you go along too like "ok this sounds like this if I use a saw wave, how would it sound if I used a sine instead?" stuff like that. You just mess with everything and try out new things that are out of the norm when you are sound designing.