Can you apply more coats if you have product left over? How many coats can you apply?
Also while preparing the paint, after clay, can I use Zaino Z5 to get existing little swirls out made by dealer? I'll use alcohol to take it our later. Then cquartz.
Any advice?
Absolutely, you can apply more coats. I imagine you will start getting diminishing returns but 2-3 coats would be great.
And yes, doing a one step paint correction after clay bar is highly recommended. You've got a good plan.