Great replies by Matt there .The DA machine and rotary are explained very well in DW i definately recommend reading it in fact its a must tbh.
Both machines are very capable and have their own place for certain requirements and situations. The rpm,s can be the same but dual action wont spin on one axis like the rotary , the oscillating action of the DA makes the work rate less in the area your working. This comes into its own and has many benefits as does the rotary machines. The DA i have has a higher rpm range but the rotary still cuts faster at lower rpm,s.

Claybar. Many choices out there and you can have different grades depending what you need. I have a soft, meduim and hard selection . You can marr paintwork by claying especially if the surface is highly contaminated. Machine polishing maybe required to remove any marring.Dont be shy with lubrication haha .... Decontaminating paint doesnt need to stop after claying. Paint cleansers and iron deposite removal are other forms of further decontamination.

I like Polished Bliss for certain items and free delivery , Clean your car (cyc) Autobrite , G technique, Bilthamber ,Autosmart,Meguairs , to name a few. Goto DW sign up its a very welcoming forum with stacks of info . Too much sometimes lol.