do I need overvoltage protection with 4.8V NI-MH pack?
If just you use this circuit with NiMH batteries as discribed a overvoltage protection is not needed. But it could come in handy when there is the possibility to use primary cells that might have a voltage of 1.5 V or another voltage source.

A low dropout voltage regulator for the controller supply would be a simple solution. Depending on the current drawn by your controller a series resistor and/or diode might also help.