What does the datasheet information for a switch mean?
A reed switch like this will not require any minimum voltage. It should work quite happily down to millivolt levels. If you want to switch on an LED from a 5V supply that is switched by the reed switch you will need a resistor that limits the current to no more than
20mA. The forward voltage drop over a red LED is around 2V so your resistor will drop 3V which means it needs to be at least about 150 ohms.