5-0,
I like your original idea, especially if the color of the vehicle is dark. Proper prep is the way to go!! I really don't see you getting a whole lot more of protection going PwC then EX. Personally, and especially if it is a dark car, I would go SSR2 at PC speed of 5.5-6 on a Megs Yellow pad, then SSR1 at5-5.5 on yellow also. Follow it up with EX by hand or by a PC.
I know your running a business here, so look at it from this prospective. Are you really adding "That Much" by doing PwC? IF you only wanted to do a 2-step process, you could do as Scott P said, however, this doesn't work all the time on a dark colored vehicle. I'm just trying to give you a heads up before you get your head stuck between your legs on the project. Make sure you make some $$ at it!
Take care, and I hope business is going well for you!