Well the FRPP B and C springs only drop the car about 1.25 inches in front and around .75" in the rear. The plates aren't really needed, but if you are driving several thousand miles a year I would install them. I installed some after my springs just b/c I liked the look of the plates.
Most mustangs are set up from the factory with about 0 degrees of camber. When you lower the car the negative camber will increase, usually to around 1 degree with a 1.5" drop, which is what Maximum Motorsports recommends for a performance street setting anyway. The toe is the most critical thing. When you lower the car the tires will toe OUT. It is a good idea to take the car somewhere to have the toe checked after a spring install. Too much toe in or out will quickly wear the tires.
Yes the CC plates do only what their name implies. The toe is adjusted with the tie rod ends. I did mine myself but I have the equipment. You can also just use a tape measure if you are very careful and precise. My car is toe IN 3/32", which is the distance between these two Is....I I. So you must be very precise!