What is the recommended voltage rating for the bootstrap capacitor? Why is there a 0ohm resistor in series with the bootstrap capacitor?
The 0ohm resistor in series with the bootstrap capacitor is used for EMI improvement if needed. If you need to slow down the switching rising edge, add some resistance (typically around 5-20 Ohms max).
Not always is the boost capacitor charged via diode from Vout. Depending on the part it is sometimes only charged from the internal BST regulator, often Vcc which is an LDO. In this case the voltage rating of the boost cap according to the max. internal regulator voltage is sufficient. So for a MPQ4436 style part, even if you do 24V Vout, a 10V boost cap will do. You can check the abs. max. BST pin rating (in the MPQ4436 case Vsw+6V) to get an idea.
BR
Christian