Can't answer all your questions but I can tell you what clay bars are used for. On a newly washed car, you use a lube (usually spray on) and a piece of clay (its like plastercine) and lightly rub your paint down. The clay will remove from the paint a lot of the little imperfections that washing and even waxing leaves behind. You'd be surprised, your paint can look spotless and yet 10 minutes of using a piece of clay on a body panel will leave the clay dirty. You tend to feel the benefit more than see it. You'll be amazed how much smoother a finished panel will feel than one you've not done. I'm not too sure how much benefit you get though on new paint as this shouldn't have many imperfections in it. Clay is at its best when removing the microscopic imperfections that every day use puts there (acid deposits from birds etc). Once "clayed" you need to polish and then put on a wax to protect your polish. However, on new paint you should only need the top coat of wax putting on. I'm no expert but my brother is a car detailer and he swears by American Meguirs products. A word of warning though - make sure your car washing product your using is harmonious to the wax you put on. The best wax'es are natural and a lot of car wash products will remove a natural wax after just a couple of washes.
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