1-Wire and the resistor
1) "Can I break anything if I forget the 4.7 k resistor?"

No. You might damage the external device if you drive the Arduino output active HIGH instead of high-impedance. Usually the libraries take care of this.

digitalWrite( 1 , HIGH ); pinMode( 1 , OUTPUT );  // Bad, active HIGH
digitalWrite( 1 , LOW );  pinMode( 1 , INPUT );   // Good, high impedance.


2) "Does it have to be 4.7k"?

No. Check the datasheet for details and considerations. Depending on speed and power requirements pull up resistors usually vary from 1kΩ to 100kΩ. Your 4k7 is about as good as my usual 10kΩ.