Welcome to Autopia. And to answer your questions...
1. There are loads of polishes on the market. The most popular and most user friendly for the PC7424 are the Sonus and
Menzerna range in my opinion.
2. Wash, clay, polish and wax. Preparation is the most important stage and taking your time is paramount to getting a perfect finish. If you get the polishing stage right - then you'll achieve a fantastic shine.
3.
Meguiars Quik Clay Kit is a good starters clay. Comes with clay bar and lubricant.
4. The PC7424 is a very forgiving machine in that it is very difficult to burn through paint. A rotary on the other hand is a much more complicated piece of machinery. If you are not confident enough to machine polish your own car, simply practice on scrap panels beforehand or get a pro-detailer to detail the car and simply ask if you can watch and learn.