new PU205 owner saying hello

Hi for Montreal Canada
Just received a new PU205 multi and am quite excited to start testing it.
I have not done any TIG welding before so I am not quite sure how to start.
Got the tank of Argon and some 3/32 #2 tungsten and some chemical sharpener. The first question I have is the kit has 3 cups and 3 collates with numbers on it which only 1 collate seems to fit the 3/32 tungsten. There are # on the collates how do I know which collate is for what size tungsten.
2nd_After reading through Tips and Tricks web sit I understand the cup sizing and along with the miller calculator I seem to believe that the #5 cup would be ok for 1/8 mild steel, right or wrong?.
3rd_ The kit comes with a knob, what is that for?
4th_ On mild steel is it necessary to remove the mill scale?
5th_ I am still somewhat confused with the 2T/4T/Remote switch!
Anyway Hi again, glad to join in.