No don't mix pre-workouts with Clen you'll make yourself overstimulated and sick. Your body might build up resistance to your pre-workout or even the Clen. You need to take breaks with Clen. You could use it 2 weeks on Clen, 2 weeks off Clen while using your pre-workout and continue to cycle it...
Thats going to be some ride. Your need to figure out your PCT so you can keep your gains. You also want to keep fat gain to as little as possible while doing your PCT.
Longest for me is 48 weeks. I really watched my health and was getting bloodwork every 6-8 weeks. You can't sleep on it and after being on it so long you have to adjust back. Its a great drug don't get me wrong, but look at it as a step not a staple.