1. How many iterations should be done when using the Newton-Rhapson method?

The number of iterations depends on the number of decimal places required.

2. How do I know when to stop when using the Newton-Rhapson method?

There are two ways:

If working to 2 decimal places, continue until the difference between successive iterations is < 0.01

OR

Continue until both x1 and x2 have the same value, when rounding to the desired number of decimal places.